how can you prove that a golf cart hit a parked truck and made a dent in truck?

Answer 1

Look for paint transfer on the cart and the truck. They should match up. The problem is finding the correct cart and the evidence may be gone by now. Depends on how big the damage was to both vehicles.

Answer 2

were there any surveillance cameras?

no?

if you know which cart, there should be microscopic specks of your paint on the cart - scrape them carefully into a container and have an automotive forensist make the match.