If someone has returned from a doctor's appointment, you can ask them such casual questions as:
How did it go?
What did the doctor say?
Is everything OK?
If the person doesn't want to discuss it (for example, if he got a particularly bad diagnosis), he'll probably just give a short response which indicates he doesn't want to talk about it. Otherwise, he'll be glad you asked and will tell you all about it. ("Oh, he said I have a cataract and will have to have laser surgery....")