Here are a couple of books that he may want to check out:
Advanced Options Trading: Approaches, Tools, and Techniques for Professionals Traders by Kevin Kraus
The Bible of Options Strategies by Guy Cohen
Then there is Options as a Strategic Investment by Lawrence Mcmillan that’s often considered the “Bible” of options trading, but he may have already read it if he’s looking for something more advanced.
I’m assuming here that he’s interested in options trading and strategies, not pricing.