As an above poster stated, if your trying to get a JW to think, you might want to ask THEM how the GB make dicisions. Ask them to tell you how it's done.
This is a question that all JW's should be able to answer, but none can, and most have not even thought to ask it yet.
So get him to start asking, or at least wondering.
Ask him, do they get there info in dreams? OR visions? or do they all hold hands and say a prayer and writing appears on the wall? Do all the GB come to the same conclusions all at the same time? Is there voting invoved? IF so how much of a vote does it take to win?
Since your JW will not be able to answer these questions, it can be something you can refer back to every now and then, over time as though you are still just "wondering"
I have done this with my family and it just makes them nuts because unlike most things, they have NO REPLY to such a question, none at all. They know it is a very legitimate question that any member should have an answer to.
And whats more they are embarressed that they cannot answer it, AND embarressed that they never even thought to ask it, until you started nagging them about it.