I have a 12 feet diameter wheel and a 35kwh(550rpm) PTO generator that needs 70 HP for operate properly and I will use a water pump to run the wheel, how many hp or how many GPM output should have the pump?

I think it would help to know what the volume of flow will be and is this an over shot or under shot wheel ; maybe some pictures would make things clearer

What is running the pump? You mean to suggest that you are going to turn a water wheel by pumping water onto it to generate 70HP in order to run a generator, which is to run the pump that is turning the wheel?

This sounds suspiciously like a free energy project. Unless the pump you're using to power the water wheel is solar or wind powered, and probably pumping water into a millpond-like reservoir, you really aren't going to extract more energy from that setup than you put into it.

I would love to see pictures, and a better explanation of what you're seeking to do.

-CK