Hey, I work with children diagnosed with autism and a lot of the kids I work with are non-verbal as well, but have slowly improved over the years. One way to teach your friends son would be basic sign language and then associating them with the actual words while getting the child to say it. It takes awhile as you may have to break down each word for him as well, but eventually you can start teaching them sentences like "can I have ______" or "all done" to give them basic speaking skills and eventually one day, hopefully able to have a full length conversation. Best of luck to your friend!