When you meet Korgan in the Copper Coronet and ask him to join with you, he will ask for you aid in recovering the Book of Kaza. His incentive being purely monetary. The book is located in a crypt below the Graveyard District. Enter through either location and proceed southward.
When you enter the Southern Crypt, be prepared for a large fight will all sorts of undead. This room is also full of traps, so be detecting!
After entering the tomb and finding it looted, Korgan will be upset and demand to head to Pimico's estate in the Temple District and attempt to head off his fellow conspirators. Upon entering Pimico's estate, you will find him slain. Korgan suggest going to the Slums District, a known hangout of his ex-buddies.
Go to the slums and climb to the roof of the Copper Coronet, where you will encounter the looters. Korgan will challenge them and they will attack your party. Dispatch them and you will recover the Book of Kaza, pleasing Korgan. I believe the only thing you can do with the book is sell it for a pretty decent sum.
This is a pretty quick and easy quest, well worth it to keep Korgan in your party.