If you go to the disABILITIES Board and check out the disABILITIES FAQs thread, there is a link to the official WDW Guidebook for Guests with Disabilities. That has information about the attractions that have warnings. They are also marked on the park maps with a red triangle and by signs in front of each ride and at least once before boarding.
After you know which rides have warnings, he can talk with his doctor to find out which of those the doctor feels might be OK for him despite the warning. If the doctor tells him to not go on any with warnings, there are still a lot of things to do and see at WDW.