The first time you read a given Skill Book, your level in the associated skill will be permanently increased by one point. You do not actually have to read the entire book—simply opening the book and immediately closing it again is sufficient. There are five different books for each of the 18 skills making 90 in total. Unlike trainers, there is no limit to how many skill books you can read at one level.
When you pick up a skill book, you automatically start to read it, and therefore you immediately obtain the skill bonus. You can read any skill book without it being considered theft—theft only occurs if you select to "Take" an owned book while reading it. If you want to save a skill book for later, you can ask your follower to take or steal it for you.
If you find an additional copy of a skill book that you have already read, you will not receive any skill bonus for reading the additional copy.
Skill books are only available at the places listed in the following list, or as quest rewards (e.g. Hitting the Books). They are never found in random loot, and they are never part of a merchant's inventory. Skill books can be easily distinguished from most other books simply by looking at their value, which is usually around 50 gold or higher. Most other books are substantially less. They can be sold to any merchants who trade in books, i.e. spell and general goods merchants.

TLDR; A skill book in Skyrim is a book that, when read, will level up a skill by 1 (Or 2 if you have a certain blessing or Active Effect.)

A Game at Dinner (0001AFC4) -

Dead Crone Rock (The Reach), by a lever opening the way to the rooftop
Forsaken Crypt (The Pale), in the room where The White Phial is found
Harmugstahl (The Reach), behind the locked door in the room with an alchemy lab, on a bookshelf
Honningbrew Meadery (Whiterun), in the upstairs bedroom
New Gnisis Cornerclub (Windhelm), middle floor, on top of a dresser

De Rerum Dirennis (0001AFC7) -

240 ft N of Evergreen Grove (Falkreath Hold) (map)
Grave Concoctions (Falkreath)
Sinderion's Field Laboratory (Blackreach)
The Midden Dark (College of Winterhold), at an alchemy lab
Valerica's StudyDG (Castle Volkihar), on a bookshelf east of the portal
On the body of a dead alchemist at Clearpine Pond

Herbalist's Guide to Skyrim (0001AFC8) -

Arcadia's Cauldron (Whiterun)
Boulderfall Cave (The Rift)
Journeyman's Nook (Winterhold)
The Hag's Cure (Markarth), on the shelf under the counter

Mannimarco, King of Worms (0001AFC5) -

Evergreen Grove (Falkreath Hold), on an altar
470 ft S of Haafingar Stormcloak Camp
Nightcaller Temple (The Pale), in the Alchemy Lab room
750 ft ESE of Winterhold, next to the corpse of Rundi
ESE of Winterhold, in an Apothecary's Satchel next to two skeletons

Song of the Alchemists (0001AFC6) -

Anise's Cabin (Falkreath Hold), on a table at the foot of the bed
Bards College on the library counter (after accepting Lami's request in Rare Gifts)
Apocrypha DB, Waking Dreams, Chapter III

Breathing Water (0001B236) -

Ilinalta's Deep (Falkreath Hold), underwater room, next to a submerged chest
Kraldar's House (Winterhold), in a basket on the bookshelf next to the fireplace
Snapleg Cave (Eastmarch), in one of the tents, sitting on a barrel
600 ft SSE of Steamcrag Camp (Eastmarch), at the unmarked Shrine of Akatosh
460 ft NNE of Ysgramor's Tomb (Winterhold), on a barrel near Ilas-Tei's corpse
ApocryphaDB, The Hidden Twilight, Chapter V

Daughter of the Niben (0001AFC9) -

Brandy-Mug Farm (Eastmarch), on top of the fireplace
390 ft E of Haemar's Shame (Falkreath Hold)
530 ft NE of Pale Imperial Camp, under an overturned skiff
Understone Keep (Markarth), on a table near the throne
Urag gro-Shub (College of Winterhold), Hitting the Books quest reward

Reality & Other Falsehoods (0001AFCC) -

Bthardamz Arcanex (The Reach) on Orchendor (only as part of quest The Only Cure)
Marise Aravel's House (Riften), in a basket on the top shelf of a bookcase
Snow-Shod Farm (The Rift), basement
320 ft WSW of Sundered Towers
Yngvild Throne Room (Winterhold), next to the throne

Sithis (0001AFCB) -

Cradle Stone Tower
Dark Brotherhood Sanctuary (Falkreath Hold)
Dawnstar Sanctuary (The Pale)
Nchuand-Zel (The Reach), in the central cavern
NNW of the Wreck Of The Brinehammer, in a locked chest underwater

The Lunar Lorkhan (0001AFCD) -

Cragwallow Slope (Eastmarch), central chamber
Faldar's Tooth (The Rift), on a shelf at the top of one of the outer towers
Mzulft Boilery (Eastmarch), on a table next to a skeleton behind a locked door
440 ft SSE of Pinewatch (Falkreath Hold), inside a tent
Solitude Lighthouse (Solitude), Mazoka's quarters

Father Of The Niben (0001B008) -

Hunter's Rest (Falkreath Hold), between two bedrolls.
460 ft SW of Kagrenzel (Eastmarch).
190 ft NNE of Twilight Sepulcher (Falkreath Hold).
Wreck Of The Brinehammer (The Pale), lower cargo hold.
Autumnshade Clearing, on the corpse of a dead hunter.

The Black Arrow, V2 (0001B009) -

Brood Cavern (Hjaalmarch), on the corpse of a dead hunter
The Drunken Huntsman (Whiterun), under the counter.
Helgen Keep (Falkreath Hold), on the counter in the torture chamber, where the torturer is encountered during Unbound.
Robber's Gorge (Hjaalmarch), on the table in the cabin at the top of the hill.
Valtheim Towers (Whiterun Hold), top of the north tower.

The Gold Ribbon of Merit (0001B005) -

Angi's Camp (Falkreath Hold), inside the shack, on the end table by the bed.
300 ft SE of Autumnshade Clearing, in an unmarked hunter encampment, under a tent.
Fletcher (Solitude), on the low table immediately to your left upon entering.
Fort Hraggstad (Haafingar), over the table in the west room.
290 ft N of North Cold Rock Pass, in an unmarked hunter encampment, under the tent.
Apocrypha DB, Untold Legends, Chapter IV.

The Marksmanship Lesson (0001B26D) -

Cliffside Retreat (The Reach), on a table.
Dawnstar Sanctuary (Dawnstar), on the table with the map.
Faldar's Tooth (The Rift), kitchen area.
Gilfre's House (Eastmarch), on the table on the right after entering.
Jorrvaskr Living Quarters (Whiterun), inside a display case in Aela's room.


Vernaccus and Bourlor (0001B007) -

Clearspring Cave (The Rift)
Froki's Shack (The Rift)
Graywinter Watch (Whiterun Hold), on a barrel
Knifepoint Ridge, near the forge.
The Treasury House (Markarth), on a circular ledge with a pot on the west side of the main room

A Dance In Fire, v2 (0001AFDF) -

Fort Snowhawk (Hjaalmarch), on a table in the room west of the back entrance in the main keep
Karthspire Camp, over a crate inside one of the lower tents
380 ft SE of Stendarr's Beacon (The Rift)
Traitor's Post, on a cupboard
Carried by a bandit during the freeform event triggered at Kjenstag Ruins

Battle of Red Mountain (0002F83C) -

Largashbur Cellar (The Rift)
Skybound Watch Pass (Falkreath Hold), on a shelf near a chest
Kilkreath Ruins (Haafingar), in a corner bookcase before activating the last beacon there
Tolvald's Crossing (The Rift)
In an unmarked, destroyed shack WSW of Shor's Stone and SE of Rift Watchtower, on a table in the back near the fireplace (this unmarked location is known as Redwater Den in the Dawnguard plug-in)

Death Blow of Abernanit (0001AFDD) -

430 ft W of Dawnstar
Jarl's Longhouse (Falkreath), left room of the bottom floor on a table
Northwind Mine (The Rift)
180 ft WSW of Reachwater Rock, (The Reach), in an unmarked Forsworn camp
Hall of the Dead (Whiterun), found inside the Catacombs on a table in the first room to the left
ApocryphaDB, Epistolary Acumen, Chapter III

The Mirror (0001AFDE) -

Broken Tower Redoubt (The Reach), on bookshelf in the sleeping area
Forsaken Cave (The Pale), over a table in the first tomb's zone
After accepting Captain Aldis' request during Rare Gifts: Palace of the Kings Upstairs, in the northernmost sleeping room

Warrior (0001AFE0) -

Driftshade Refuge (Winterhold), near the fireplace in the boss's chamber
Fort Kastav Captain's Quarters (Winterhold)
380 ft SSE of Haafingar Stormcloak Camp
280 ft WNW of North Skybound Watch, by a bedroll in an unmarked bandit camp
Silent Ruin (Blackreach)

2920, Frostfall, v10 (0001AFEA) -

Belyn Hlaalu's House (Windhelm), upstairs behind the dresser.
450 ft SSW of Evergreen Grove (Falkreath Hold), on an unmarked necromancer's altar.
Ironbind Barrow (Winterhold) on Beem-Ja (only as part of quest Coming of Age).
Sunderstone Gorge (Falkreath Hold), on a pedestal in the room with the word wall.
On a summit south of Geirmund's Hall, carried by a necromancer

2920, Hearth Fire, v9 (0001AFE9) -

640 ft SE of Angi's Camp (Falkreath Hold).
520 ft N of Pinewatch (Falkreath Hold).
The Mortar and Pestle (Dawnstar), under the counter.
Rimerock Burrow (Haafingar), on an end table in the final cavern.
Urag gro-Shub (College of Winterhold), Hitting the Books quest reward.
ApocryphaDB, The Hidden Twilight, Chapter V.

Liminal Bridges (0001AFE8) -

Broken Tower Redoubt (The Reach), the topmost tower (the Briarheart's room)
Falkreath Watchtower, at the top of the stairs at the entrance to the tent
2 copies in Shalidor's Maze in Labyrinthian (Hjaalmarch)
east of Sleeping Tree Camp, on the body of a dead conjurer upon an altar

The Doors of Oblivion (0001AFE7) -

Fellglow Keep (Whiterun Hold), podium in far west room
Hall of the Dead (Falkreath), under the bed next to the left-hand wall
Ilinalta's Deluge (Falkreath Hold), in the first room, on northwest table
Reachcliff Cave (The Reach)
120 ft SSW of Sightless Pit (Winterhold)

The Warrior's Charge (0001AFEB) -

Brittleshin Pass (Falkreath Hold), near the Arcane Enchanter
620 ft NE of Pinepeak Cavern (The Rift)
310 ft N of Southfringe Sanctum (Falkreath Hold)
Stillborn Cave (Winterhold)
Understone Keep (Markarth), Jarl's quarters, on the end table nearest the bed

A Hypothetical Treachery (0001AFEE) -

Aretino Residence (Windhelm), behind the bookshelf
Fellglow Keep (Whiterun Hold), on a table in the storeroom
High Gate Ruins (The Pale), central chamber
580 ft NW of Windward Ruins (The Pale)
between Sleeping Tree Camp and North Brittleshin Pass, in a chest down a grate opened by solving a puzzle
Volkihar UndercroftDG, on a table in the room with the lever for the first bridge
ApocryphaDB, The Hidden Twilight, Chapter V

Horror of Castle Xyr (0001AFEC) -

210 ft WSW of Darklight Tower (The Rift)
Glenmoril Coven (Falkreath Hold), northwestern chamber, in a box under a tent
350 ft SE of Harmugstahl (The Reach)
Rannveig's Fast (Whiterun Hold), in Sild the Warlock's room on a table
480 ft SW of Stendarr's Beacon (The Rift), outside burning house under fallen tree

Mystery of Talara, v3 (0001AFF0) -

Birna's Oddments (Winterhold), upstairs on a dresser
Darklight Chambers (The Rift)
Morvunskar (Eastmarch), on a bookshelf in the northeast corridor
Steepfall Burrow (Haafingar), in the room with the large chest
Tolvald's Crossing (The Rift)

Response to bero's speech (0001AFED) -

Haemar's Cavern (Falkreath Hold), on a desk near two dead bandits
Iron-Breaker Mine (Dawnstar)
Thaumaturgist's Hut (Morthal)
Witchmist Grove, under the bed in the cabin
Urag gro-Shub (College of Winterhold), Hitting the Books quest reward

The Art of War Magic (0001AFEF) -

Southfringe Sanctum (Falkreath Hold) on Bashnag (only as part of quest The Savior of Selveni Nethri)
540 ft SW of Bthardamz (The Reach)
Ravenscar Hollow (Haafingar), on a table
The White Hall in Dawnstar (The Pale)
ApocryphaDB, Waking Dreams, Chapter VI

A Tragedy in Black (0002F838) -

Bruca's Leap Redoubt (The Reach), on the bookshelf
East of Eldergleam Sanctuary, on a crate surrounded by soul gems
Glenmoril Coven (Falkreath Hold), on a table next to an Arcane Enchanter
Ilinalta's Deep (Falkreath Hold), in the room with the Arcane Enchanter and Alchemy Table
240 ft ENE of Twilight Sepulcher (Falkreath Hold) at a Shrine of Akatosh

Catalogue of Armor Enchantments (0002F83B) -

The Brinehammer Below Deck (The Pale)
Falion's House (Morthal), on a shelf
Fort Amol (Eastmarch), on the cupboard next to the Arcane Enchanter
Steamscorch Mine (Eastmarch), on a table just after entrance
Shrine of Mehrunes Dagon

Catalogue of Weapon Enchantments (0002F83A) -

Castle Dour, Emperor's Tower (Solitude)
Darkwater Pass, near the middle of the dungeon, found on top of the Arcane Enchanter
Roadside Ruins (Falkreath Hold), near a chest in the center
The White Hall (Dawnstar)
Urag gro-Shub (College of Winterhold), Hitting the Books quest reward
ApocryphaDB, Waking Dreams, Chapter III

Enchanter's Primer (0002F837) -

Carlotta Valentia's House (Whiterun), on the bedroom floor
410 ft NNW of Fort Kastav (Winterhold)
Honeyside (Riften)
Hob's Fall Cave (Winterhold), on the Arcane Enchanter
530 ft NNE of Valthume

Twin Secrets (0002F839) -

Calcelmo's Laboratory (Markarth)
Jarl's Longhouse (Winterhold), inside a basket in the southwest corner of the Jarl's bedroom.
Serpent's Bluff Ruins (Whiterun Hold), on the Arcane Enchanter at the end of the dungeon.
Shrine of Stendarr, south of Swindler's Den
Treva's Watch (The Rift), bandit chief's room

2920, MidYear, v6 (0001AFF7) -

Blackreach, over a stone table in the south zone.
Bonechill Passage (Falkreath Hold), on the ground in the first room when entered.
320 ft ENE of Cradlecrush Rock (Eastmarch) at a Shrine of Talos.
Fort Dunstad Prison (The Pale).
Guardhouse (Morthal), behind the barrel to the right of the fireplace.

Chimarvamidium (0001AFF8) -

Skill books:
Calcelmo's Tower (Markarth)
Goldenrock Mine (Eastmarch), near a bedroll in a dead end tunnel
Reachwind Eyrie (The Reach), on a desk as you enter
Between the Wreck of The Pride of Tel Vos and Bleakcoast Cave, under a fallen tree
On the corpse of a Stormcloak soldier in a troll den northeast of Ivarstead by the river
Ordinary books:
Alftand Glacial Ruins (Winterhold), under a pot on a barrel in the bloody part of the cave with a fireplace and several bedrolls
Calcelmo's Laboratory (Markarth)
Dwemer Museum (Markarth), in an adept-locked display case
Septimus Signus's Outpost (Winterhold), on the bookshelf

Hallgerd's Tale (0001AFF6) -

530 ft NNW of Fallowstone Cave (The Rift)
Jorrvaskr (Whiterun), on an end table in the main hall, opposite the fragments of Wuuthraad
Mistwatch East Tower (Eastmarch), on a dresser in the bandit leader's room
Rift Watchtower, top of the tower
As long as the Falkreath Stormcloak Camp is disabled: Between Orphan Rock and Haemar's Shame on the body of a dead Nord
Alor HouseDB (Raven Rock), downstairs in the southern bedroom

Orsinium and the Orcs (0001AFF9) -

Darkshade (Whiterun Hold), second room, lying near the water
Dushnikh Yal Cellar (The Reach)
Fort Fellhammer Mines (Winterhold), on a table near the bottom of the mine
Lost Knife Hideout (Eastmarch), on a table near a sleeping guard, in the collapsed fort section
Rockwallow Mine (Hjaalmarch), atop the mine scaffolding
ApocryphaDB, Epistolary Acumen, Chapter III

The Knights of the Nine (0001AFFA) -

Guldun Rock Cave (Whiterun Hold)
Hall of the Vigilant (The Pale), downstairs area
Mauhulakh's Longhouse (Eastmarch)
Palace of the Kings Upstairs (Windhelm), first room on the left upstairs, top shelf of cupboard
220 ft N of The Tower Stone, next to a skeleton and a flag

2920, Sun's Dawn, v2 (0001B010) -

Ansilvund Burial Chambers (Eastmarch), in the second section, large room with the hanging cages, on a pressurized pedestal.
Darklight Tower (The Rift), near the entrance to Darklight Chambers, on a table.
Movarth's Lair (Hjaalmarch), in the part of the cave accessed via the passage to the left of Movarth's throne, on an end table.
Temple of Dibella, Inner Sanctum (Markarth), on the lowest shelf of a bookcase in a long row of books.
On an island between Reachcliff Cave and Old Hroldan Inn (The Reach), at the top of a waterfall cliff, in an apprentice-locked chest.

Before the Ages of Man (0001B012) -

Angarvunde Ruins (The Rift), on a table with embalming tools
Dragonsreach Jarl's Quarters (Whiterun)
Reeking Cave (Haafingar), in the frost troll hideout
Shroud Hearth Barrow (Ivarstead), on a stone altar near the entrance
Skytemple Ruins
ApocryphaDB, The Hidden Twilight, Chapter V

Incident at Necrom (0001B00F) -

Bloodlet Throne (Falkreath Hold), in the jail cell
270 ft NW of Fallowstone Cave (The Rift), under a tree north of the road
Pinemoon Cave (Haafingar), at the cave's far end
at the unmarked Shrine of Dibella south of Dawnstar
southeast of the Shrine to Peryite, in a chest next to a dead Wood Elf

Mystery of Talara, Part 4 (0001B013) -

Blind Cliff Bastion (The Reach), on the platform near the large chest
Broken Fang Cave (Whiterun Hold), near Arcane Enchanter
Hag's End (The Reach), in the room where the bridge is activated
Nepos's House (Markarth), in northeast bedroom by candelabra
Stony Creek Cave (Eastmarch)

The Black Arts On Trial (0001B011) -

Falkreath Jail (Falkreath)
370 ft SSE of Hillgrund's Tomb (Eastmarch)
500 ft SE of Morthal
The White Phial (Windhelm)
Urag gro-Shub (College of Winterhold), Hitting the Books quest reward

Ice and Chitin (0001B001) -

Guard Tower (Markarth), in the northeast corner on a wooden table
410 ft NNW of Narzulbur
Shrouded Grove Cave (The Pale)
Snow Veil Sanctum (Winterhold), final room
Windhelm, guard's room under the bridge outside the city, between the gate and the stables

Jornibret's Last Dance (0001B002) -

Autumnwatch Tower (The Rift), top floor of the small tower
Fort Neugrad (Falkreath Hold), in the library
190 ft SE of Honeystrand Cave (The Rift)
Korvanjund Temple (The Pale)
Soljund's Sinkhole (The Reach)

Rislav The Righteous (0001B004) -

160 ft W of Abandoned Prison (Eastmarch), in the debris surrounding a cabin crushed by a fallen tree
420 ft S of Bleakcoast Cave (Winterhold)
Cracked Tusk Vaults (Falkreath Hold)
Fort Greymoor (Whiterun Hold), second-floor training room
Riverside Shack

The Rear Guard (0001B000) -

Castle Dour (Solitude), downstairs
Driftshade Cellar (Winterhold), in the room before the ice tunnel
Druadach Redoubt Cave (The Reach), near the fire pit
240 ft WSW of Largashbur (The Rift)
480 ft SE of Shadowgreen Cavern
ApocryphaDB, Untold Legends, Chapter IV

The Refugees (0001B003) -

Blind Cliff Cave, in the collapsed tower
West of Helgen and south of The Guardian Stones, at an unmarked bandit camp
Solitude Blacksmith (Solitude), in the upstairs bedroom on a wall shelf above some candles
Wolfskull Ruins (Haafingar), on the ritual altar atop the highest tower
Between South Cold Rock Pass and Drelas' Cottage, on the corpse of a dead hunter

Advances in Lockpicking (0001B01C) -

390 ft ENE of Angarvunde (The Rift), next to a dead Redguard
Bannermist Tower, on a table just below the top
Chillwind Depths (Hjaalmarch), over a table in the innermost room
The Ragged Flagon - Cistern (Riften), on a barrel in the training room
Sewer (Riften), on a barrel behind a grille
ApocryphaDB, Untold Legends, Chapter IV

Proper Lock Design (0001B01B) -

Cidhna Mine (Markarth), next to the Evidence Chest
Faldar's Tooth on a table at the top of one of the outer towers
490 ft SSE of Largashbur (The Rift)
Twilight Sepulcher (Falkreath Hold)
southeast of Steepfall Burrow, on a corpse next to two dead deer

Surfeit of Thieves (0001B01D) -

Mistveil Keep Jarl's Chambers (Riften)
Pelagius Wing (Blue Palace, Haafingar), in the cellar room
Potema's Catacombs (Haafingar), only while on the quest The Wolf Queen Awakened
Volskygge (Haafingar), just right of the stone door
Wreck of the Winter War, second level

The Locked Room (0001B019) -

Alftand Animonculory (Winterhold), in the treasure room
Southeast of The Apprentice Stone, near a chest in half-flooded building
Cronvangr Cave (Eastmarch)
Highmoon Hall (Morthal), on a bookshelf in the room upstairs (right-hand side)
Honeystrand Cave, on a bandit corpse guarded by bears

The Wolf Queen, v1 (0001B01A) -

Broken Fang Cave (Whiterun Hold)
Cragslane Cavern (Eastmarch), behind the bar
Dawnstar Jail (Dawnstar), inside the jail cell
Duskglow Crevice (The Pale)
South of Snow Veil Sanctum, west of Yngol Barrow

2920, Morning Star, v1 (0001AFD9) -

Driftshade Refuge (Winterhold), on a table in the final room with the barred door
Jorgen and Lami's House (Morthal), in a bucket on top of the barrel to the left of the bed
Lost Echo Cave (Falkreath Hold), on the altar
Northwatch Keep (Haafingar), behind the bar
Sabre Cat den between Broken Tower Redoubt and Crabber's Shanty, on the body of a dead hunter
Next to a bed roll at Dayspring Canyon, at the top of Fort Dawnguard DG

Fire and Darkness (0001AFDA) -

Dawnstar Sanctuary, basement
Folgunthur (Hjaalmarch), lower level
480 ft ENE of Moss Mother Cavern (Falkreath Hold)
The Ratway Warrens (Riften), in Esbern's room
320 ft SW of Wreck of The Pride of Tel Vos (Winterhold)
ApocryphaDB, Epistolary Acumen, Chapter III

Mace Etiquette (0001AFE6) -

Fort Greenwall Captain's Quarters (The Rift)
Orotheim (Hjaalmarch), on a crate near the grindstone
Sky Haven Temple (The Reach)
Uttering Hills Cave (Eastmarch), on an east-facing bookshelf in the northernmost set of rooms
Volunruud (The Pale), on the throne in the northwest room

Night Falls on Sentinel (0001AFE4) -

310 ft S of The Guardian Stones (Falkreath Hold), in a tent in a bandit camp
Volunruud (The Pale), in boss chest (only as part of quest Silenced Tongues)
After accepting Rustleif's request during Rare Gifts: Swindler's Den, on a crate

The Importance of Where (0001AFE3) -

Brina's House (Dawnstar)
Chillfurrow Farm (Whiterun Hold), on a dresser in bedroom
Gallows Rock (Eastmarch), in the Tower (Silver Hand Hideout) upstairs on table after some tanning racks
Guard Tower (Markarth), on a stone table in the north room
At a Shrine of Talos, on the island directly west of Winterhold

Aevar Stone-Singer (0001ACE6) -

Lost Valkygg, southern room
530 ft N of Nilheim (The Rift), surrounded by three barrels
Sightless Pit (Winterhold)
Thonnir's House (Morthal)
620 ft SW of Whitewatch Tower (Whiterun Hold), in a bandit camp

Beggar (0001AFD6) -

Haelga's Bunkhouse (Riften), on a counter upstairs
Ironback Hideout, on a table in the ruined house
The Ratway (Riften), on a table in the room next to the bridge
1170 ft NE of Wreck of the Winter War, next to a skeleton
between Swindler's Den and Gjukar's Monument, on the body of a dead bandit next to a Nirnroot plant
ApocryphaDB, Untold Legends, Chapter IV

Guide to Better Thieving (0002F836) -

Fort Sungard Oubliette (The Reach), down the hole
Goldenglow Estate Sewer (The Rift), by a skeleton in a side room with an Adept lock
Jarl's Longhouse (Falkreath), right room of the bottom floor locked in a display case with an Expert lock
Mara's Eye Den (Eastmarch), in a box with several other books by a stone pillar
Snowy Sabre Cat den northeast of the Thalmor Embassy gate, on the body of a dead Argonian

Purloined Shadows (0001B022) -

NW of Bonechill Passage (Falkreath Hold), in a hut under the bed
Duskglow Crevice (The Pale), in the junk room
280 ft WNW of Folgunthur (Hjaalmarch), at small campsite underneath an overhang
Honorhall Orphanage (Riften), in Constance's bedroom
Nightingale Hall, in the living quarters, on an end table next to a bed

Thief (0001AFBF) -

Argonian Assemblage (Windhelm), on a dresser
Bleak Falls Temple (Falkreath Hold), just beyond the first glyph puzzle
630 ft WSW of Ivarstead
Silverdrift Lair (The Pale)
Swindler's Den (Whiterun Hold), by a bedroll in the easternmost room

2920, Rain's Hand, v4 (0001B017) -

Blind Cliff Bastion (The Reach) on Petra (only as part of quest The Affairs of Hagravens).
Falion's House (Morthal), on a table.
Hall of the Dead (Markarth), on the shelf next to the priest's bed.
370 ft NNE of Journeyman's Nook (Winterhold), at the end of a crevasse.
Behind Widow's Watch Ruins (Haafingar).

Mystery of Talara, v 2 (0001B018) -

Eldergleam Sanctuary, leaning on the rock next to a backpack
Frostflow Lighthouse (Winterhold), on a dresser
Ragnvald Crypts (The Reach), over a table behind a chest
Ustengrav (Hjaalmarch), stone shelf near all the urns
Crystaldrift Cave, on the dead body of Gadnor

Racial Phylogeny (0001B015) -

Avanchnzel Animoncultory (The Rift), in a room on the eastern side, on the northern table
on an altar in the middle of Boulderfall Cave, Autumnshade Clearing, and Shor's Stone (The Rift)
Corpselight Farm (Falkreath) on a book shelf
Moorside Inn (Morthal), inside a basket
Urag gro-Shub (College of Winterhold), Hitting the Books quest reward
ApocryphaDB, The Hidden Twilight, Chapter V

The Exodus (0001B016) -

Forelhost Crypt (The Rift)
The Frozen Hearth Cellar, wedged between a pillar and a crate on the west wall (Winterhold)
Hob's Fall Cave (Winterhold), on a table near the Alchemy Lab
Stendarr's Beacon, on a bedroll
In a small, unmarked campsite directly between Solitude's docks and The Apprentice Stone

Withershins (0001B014) -

Arcwind Point, at a pedestal the top of the tower after progressing through the ruins
Gloomreach Cavern (The Reach)
240 ft N of Harmugstahl (The Reach)
Temple of Kynareth (Whiterun)
Valthume (The Reach), in an alcove of a room south of the large room with pews

Cherim's Heart (0001AFD1) -

Broken Oar Grotto (Haafingar)
360 ft WSW of Eldergleam Sanctuary (Eastmarch), on a table in a hunter's camp
Morvunskar (Eastmarch), next to the forge at base level
Purewater Run (The Reach), inside an underwater chest
Quicksilver Mine (Dawnstar)

Heavy Armor Forging (0001AFD2) -

East Empire Company Warehouse
Gloombound Mine, just outside the mine entrance
Pinepeak Cavern (The Rift)
Whistling Mine (Winterhold)
ApocryphaDB, Waking Dreams, Chapter II

Last Scabbard of Akrash (0001AFCF) -

330 ft SSE of Black-Briar Lodge
Fort Sungard Muster (The Reach), in the armory
Gallows Rock (Eastmarch), near the sleeping quarters

Light Armor Forging (0001AFD0) -

Cracked Tusk Keep, near the forge
Embershard Mine (Falkreath Hold), on a table in the forge area
Lod's House (Falkreath), in the basement on a barrel
Silent Moons Camp (Whiterun Hold), near the Lunar Forge
In a chest inside a pit on unmarked location east of Dushnikh Yal, south of Reachcliff Cave

The Armorer's Challenge (0001AFCE) -

Bilegulch Mine (Falkreath Hold)
Mor Khazgur (Haafingar), near the forge
The Scorched Hammer (Riften), in between the dresser and the safe
The Skyforge in Whiterun, on the stone slab to the right
Tower of Mzark (Winterhold), in first room

2920, Last Seed, v8 (0001B01F) -

Hag Rock Redoubt Ruin (The Reach), over the table.
Raldbthar (The Pale), near Alain Dufont.
Redoran's Retreat (Whiterun Hold), on a crate in the back cavern.
480 ft E of Stendarr's Beacon (The Rift), next to a bed roll.

Legend of Krately House (0001B021) -

Black-Briar Lodge (Riften), master bedroom
300 ft N of Halldir's Cairn (Falkreath Hold)
Nightgate Inn Cellar (The Pale)
Potema's Catacombs (Haafingar), in boss chest (only as part of quest The Wolf Queen Awakened)
Red Wave (Solitude)

Sacred Witness (0001B020) -

Dawnstar Sanctuary
Dark Brotherhood Sanctuary
Deepwood Redoubt, in Deepwood Vale, near the Alchemy Lab
Twilight Sepulcher (Falkreath Hold)
southeast of the Abandoned Shack, on the body of a dead Draugr

The Red Kitchen Reader (0001AFD5) -

Frostmere Crypt (The Pale), inside the ruins, on a bookshelf
New Gnisis Cornerclub (Windhelm), under the staircase on the ground floor
Nightingale Hall
Pinewatch (Falkreath Hold), secret basement
Riftweald Manor (Riften), secret basement
Valerica's StudyDG (Castle Volkihar), on a bookshelf east of the portal

Three Thieves (0001B276) -

280 ft SE of Angi's Camp (Falkreath Hold)
Honningbrew Basement (Whiterun), only during Thieves Guild quest Dampened Spirits
160 ft S of Shor's Watchtower (The Rift)
Snow Veil Catacombs (Winterhold), only during Thieves Guild quest Speaking With Silence
ApocryphaDB, Filament and Filigree

2920, Second Seed, v5 (0001B025) -

East of Gjukar's Monument at a Shrine of Zenithar.
Sadri's Used Wares (Windhelm), under the counter.
Shriekwind Bastion (Falkreath Hold), on a rock pedestal in the Master Vampire chamber, after the fire corridor.
Sorli's House (Hjaalmarch).
ApocryphaDB, The Sallow Regent.

A Dance in Fire, v6 (0001B00D) -

Dainty Sload (Haafingar)
Dead Man's Drink (Falkreath), under the counter
Debate Hall (Blackreach)
380 ft SW of Great Lift at Mzinchaleft, west of Frostmere Crypt on a cart
Meeko's Shack (Hjaalmarch), on a barrel

A Dance in Fire, v7 (0001B00E) -

Outside Angarvunde, on a table
Arnleif and Sons Trading Company (Markarth), on a crate on the west side of the sales desk
Beggar's Row (Riften), on the floor
Mzinchaleft, in Maluril's room (Hjaalmarch)
North of Sunderstone Gorge, on the body of a dead Khajiit next to the road

Biography of the Wolf Queen (0001B023) -

Blue Palace (Solitude), Jarl's bedroom
Bthardamz Dwelling (The Reach)
Liar's Retreat (The Reach), over a stone in the wall of a room
Anga's Mill Common House (The Pale), on an end table by some loose gold near a bed
Belethor's General Goods (Whiterun), on a shelf to left of counter, next to a sack

The Buying Game (0001B00A) -

Bards College (Solitude), in one of the classrooms
Dead Men's Respite (Hjaalmarch), easternmost point
East Empire Company Warehouse (Haafingar)
As long as the Falkreath Stormcloak Camp is disabled: road east of Helgen on a cart
Shrine to Peryite, on a table next to the Alchemy station

Battle of Sancre Tor (0001AFDC) -

Bleakcoast Cave (Winterhold), on the body of a dead conjurer
Broken Helm Hollow (The Rift)
Dustman's Cairn (The Reach), on the table in the first room
House of Clan Battle-Born (Whiterun), west bedroom downstairs on a shelf
Old Hroldan Inn (The Reach)

King (0001AFE5) -

Bleakwind Bluff, next to the cairn
270 ft SSW of Froki's Shack (The Rift) at a Shrine of Talos
The Katariah, at the stern of the ship
Small, unmarked ruin north of Forelhost, southwest of Black-Briar Lodge, carried by a bandit
Penitus Oculatus Outpost, on an end table, only after starting the quest Destroy the Dark Brotherhood!

Song Of Hrormir (0001AFDB) -

Abandoned Prison (Eastmarch), in a storage room filled with books and a Master-level chest
Jala's House (Solitude)
Jorrvaskr Living Quarters (Whiterun), in the basement at the end of the hall
Mauhulakh's Cellar (Eastmarch)
Yngol Barrow (Winterhold) in boss chest (only as part of quest Yngol's Barrow)

The Legendary Sancre Tor (0001AFE2) -

580 ft ENE of Broken Tower Redoubt (The Reach)
350 ft SW of Cragwallow Slope (Eastmarch)
Falkreath Barracks (Falkreath)
Northwatch Keep (Haafingar), lower level bedroom
Ysgramor's Tomb (Winterhold), only accessible during the quest Glory of the Dead

Words and Philosophy (0001AFD8) -

Geirmund's Hall (The Rift), in the boss treasure room, on a bookshelf
Lost Knife Cave (Eastmarch), on a table on the platform in the large flooded room
Mistveil Keep Barracks (Riften), on top of a dresser in the SW corner of the second floor
Shrine of Talos west of Saarthal, on the altar
Silverdrift Lair (The Pale)
ApocryphaDB, The Winds of Change

~Achievement~

Reader (20 points/Bronze) — Read 50 Skill Books

To unlock this achievement 50 different skill books must be read, out of the 90 available.

Books count towards this achievement even if they are read after the related skill has reached 100.

In this case, no message appears on screen informing you that you have read a new skill book, but the game's counter is still increased.

You can track your progress towards the achievement using the "Skill Books Read" statistic on the General page of your journal's General Stats.

~Bugs~

-On rare occasions, reading a skill book will report the skill being leveled, but not actually increase the skill's level. Being close to leveling the skill may increase the likelihood of this happening.

Save your game and check the skill's value before reading any books. If it doesn't increase after reading, reload the save and increase the level of the skill before reading the book.