As far as recovery, that is up to your son, and I wouldn't ask. Perhaps ask about things that do not concern recovery, such as gardening, tv, weather, relatives, kids. I am sure they are trying to get their lives back to normal. How about asking how the wife is? Therapy is their business. The idea is to care about them, but stay out of the recovery process. So hard, I know.
just my own thoughts,
jeepgirl