It is held by a bonus boss in the Alram Highlands. After going through the mines there's a path north that leads to a save circle. Beating the boss will get you the book.
That book is located in a mine within the Alram Highlands (North). If you ensure one of your party members has at least 30,000 HP and equips the "Final Nut," you can end the battle before the boss uses any skills, thereby bypassing its combat mechanics entirely.
