Books of Knowledge are Wealth that you can find in any region of Norway or England in Assassin's Creed Valhalla. They represent the various skills that Eivor can use to fight. There are two categories: melee and sitance.
These skills can be an aid in concealing your character for assassinations or, if you prefer, a way to deal heavy damage like a beast. You'll be able to equip four skills of each category, so you'll have to make a choice.
Note that it's possible to increase the level of your ability by learning a similar book of knowledge.
Book of knowledge in Suthsexe
Improvement: Powder can now be ignited twice.
Improvement: No detection remains in the event of a successful assassination.
Original content by Camille"Effylia" Bouin.