Dive of the Valkyries
This Book of Knowledge is located in Lolingestone Bandit Camp. You’ll need to head into the main hall of the villa then climb up onto the hanging wooden platforms then make your way over to the book of knowledge.
Thorn of Slumber
This Book of Knowledge is located within Dover Fortress. The Book is found within a small locked building at the base of the tall tower at the top of the fortress. A letter next to the locked door suggests that the key is somewhere in the tower. If you use Odin’s Sight you’ll discover that the key is at the top of the tower, so you’ll need to head all the way up to grab the key to then gain access to the book of knowledge.