I think Racheal nailed it pretty good.
This is what I would do..
Just start at the beginning with this question..
When did you find out you were going to Synonan?
Then start letting the process take its own natural course. Don't feel obligated to be trapped to a arbitrary set of questions. Sure at some point you want to steer the discussion in a direction of your liking, but for the most part you want to ease him into a comfortable enough state to let him conversate freely about his experiences.
Just keep asking him simple questions.
Why?
What?
When?
How?
Where?
Who?
Personally what I definitely want to know is the following:
1) Stage/level systems...
2) Consquences/interventions... did synonan have them or not?
3) Living arrangements...
4) Dining Arrangements..
5) Recreational activities...
6) What sort of contact was allowed with family?
7) Staff.. qualifications.. etc.. find out about these jazbos.. not so much who where they, but more like what sort of desirable qualities where sought in a Synonan staffer. I think most of their staff came from within the programme, but I'd still like to know what they looked for in a staff member. Did they have educational requirements, or did they just go for the biggest programme zombie?

Medical services.. how were those needs attended to.. Did they have a doctor or nurse on location? Did they transport to offsite medical facilities... What process did they have to go through to obtain medical help?
9) How did a person leave/graduate Synonan? Could they get out early, and what was the general concencous of those who bailed out early?
I've a few more questions, but if you can get those answered that would be a great start. Remember, just sit down and try to turn it into a casual conversation. This way the gentleman will feel more at ease and more likely to divulge information of all sorts.