Actually, do you have Korgan in your party?
(Spoiler ahead)
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The book is suppose to be in the Southern tombs of the lower crypts in the graveyard district, but when you get there you will find that it has been looted already.
Next you will have to travel to a house in the temple district (Pimlico Estate), which then Korgan will try to get you to go to the Copper Coronet. Kill the thugs on the roof top and you will find the book on one of their bodies.

I can't find the Book of Kaza. I know it's somewhere in the lower crypt of the Graveyard District (where Bohdi was?)

Can you use this book for something after getting it besides selling it?

Used sparingly, it'd probably last a good month or so in the privy.

Well, maybe for Korgan with his cheeks of leather, but I prefer something more bendable than five hundred years old parchment back there.

Just sell it.

Just be careful. I accidentally used the Book of Infinite Spells once. Couldn't sit down for a week.