I don't know of any book entirely devoted to old work. Perhaps someone else does. I always recommend Wiring Simplified because it's a good general book for the beginner. It does have a chapter with the basics of old work.

"Wiring Simplified" is a good book, and the one I first learned from many years ago. However, if you want the flat-out best book I've since seen on wiring, it's "Wiring a House" by Cauldwell. It has many photos, drawings, tables, and practical advice and tips, and is incredibly clearly written.

I also agree with David that you're not going to find a book devoted to old work. What you want to do is replace the K&T with modern wiring that meets code. From my point of view, what you need to know about K&T is that you pull the fuse or throw the breaker for the circuit you plan to work on, and then you replace the K&T wiring with modern wiring.

One other reason I'm recommending the Cauldwell book to you is that it sounds like your wiring is not to code if you have K&T connected up to upgraded circuits. The book has all the info you will need to make you confident about what's required and how to do it. Good luck.

Here is a link that might be useful: Wiring a House

I agree with kudzu_9. "Wiring a House" by Rex Cauldwell is far and away the best book i've read for beginners and people needing a quick reference or refresher. The latest revised edition is great.

"Your Old Wiring" by David Shapiro. Excellent book on wiring in older houses.