This might be a ridiculous question, but I have been watching Prince picking lately and I see him thumb is down a lot. Does anyone know if he flat picks or he does he use the side of the pick with his thumb down?

This is a really good question, I just don't know the answer

but if I had to go off the sound, I would guess he alternates between flat, and chicken picking, maybe getting a little of the flesh from the thumb on solos a little.. maybe

Thanks I was especially watching his new performance in paris and it looks like the thumb is going down

Yes, thumb is down. I noticed that a lot too.