I dont really know which book you are talking about, so i will give you both answers.
If you need the book for the Dragonspyre book quest, there should be a quest guide on Wizard101 central.
If you need the book from Halina Warhawk's Quest, then go back to her place with a few friends, then try to go through the door behind her. you will then have to fight your way to the bottom floor, where the book is (Tower of War Instance, No port ins). Since there is no port ins, and the tower is hard to solo, you want to go through the sigil with some friends.