Skill Books are unique books that grant a permanent one point increase to its associated skill. Opening a skill book will automatically grant the bonus. They can be read at any time and unlike Skill Trainers, who limit increases to five levels per level, there is no limit to the number of skill books that can be read in one level. However, the same book cannot give an additional skill bonus if read twice. The Dragonborn add-on includes an ability called Scholar's Insight that grants two points for every skill book read.
There is no tell-tale method to identify a skill book, as they look rather identical to regular books. This can often lead to the unplanned raising of a skill. However, most Skill Books for Spell Types (Destruction, Illusion, Conjuration, Restoration and Alteration) have the Spell Type's Symbol on the front cover. Occasionally, the value of the book can be an indicator or the title can often allude to what skill it may be associated with - such as with Advances in Lock Picking.
There are five different books for each skill and a total of 90 books. They can be found almost anywhere and typically appear as a world item.
Given the rarity and usefulness of skill books, it may be desired to add them to the inventory without reading them by ordering a follower to pick them up. The book can then be taken from the follower and read at a later date.
From the Guardian Stones head back up the hill slightly then head west on the road. It will be off the road on the left 100 feet or so up a dirt path. The book is on an altar.
Twilight Sepulcher - shortly after completing the trial that requires the Dragonborn extinguish the torches on either side of the Nocturnal statue, take a left which leads to a large room with a stairs down. The book is located on the desk.
Lost Echo Cave, on the table located next to the Ceremonial Braizer.
Northwatch Keep, on a shelf behind the counter in the dining area.
Unmarked sabre cat den between Broken Tower Redoubt and Robber's Gorge. It is due west of the fast travel arrival point for Robber's Gorge at some standing stones. The book is on a dead hunter's body.
Dawnstar Sanctuary, on a table just after descending the spiral staircase.
Esben's room in the Ratway Warrens in Riften, inside a box next to the bed on the right side.
Folgunthur, after entering and going down the stairs and into the first room continue through the passage and once through the passage turn left and on the wall will be the book with a dead adventurer and dead draugr.
Swindler's Den, on a crate. This book is also a quest item. Rustleif, the blacksmith in Dawnstar, asks for the retrieval of it for his pregnant wife Seren.
Mara's Eye Den, in a box with other books and a soul gem on top of the crates near the entrance.
North east of the Thalmor Embassy on a dead Argonian. Follow the cliff wall eastwards, after defeating two snowy sabre cats. The body is under an overhang.|
Avanchnzel Animoncultory, just after the ghosts talking about setting up camp there is a side door. When the door is opened, step back as blades come out of the ground. The book is sitting inside on a table.
Forelhost Crypt, go through the master locked iron cell in the middle of a room, down the stairs, through the underwater area to the north on the map. After coming out onto a dry room, go through the next underwater corridor and it will be in the next room on a shelf.
East Empire Company Warehouse, near the entrance, take the path through the shelves to reach a shelf with a stack of iron ingots on it, the book is to the right of these ingots.
South southeast of Black-Briar Lodge, from the lodge, head east up a small snowy path between the rocks, to the right at the top of the rocky slope, under a hide shield.
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