30-32psi. dont put the max pressure in the tire... will cause it to weather crack and such, maybe a little more wear in the middle of the tire.
most cars have the recommended PSI for the car on the door pillar.
Yes...they do have the reccomended PSI on the car itself, but that's for OEM tires. I really doubt he has those.
What does OEM or non-OEM tires have to do with it? It's the weight of the vehicle that sets the recommended pressure, not the size of the tire (under normal circumstances).