Is there a way to prove that you’re not tracking someone’s iPhone?

If someone has granted you the ability to track them, you can track them. If someone has NOT granted you the ability to track them, you canNOT track them. It's not like you can just start tracking someones iPhone. You or they must send you an invitation to see each others location, which has to be accepted. Thus if you haven't been given permission to know someones location, there is nothing to prove.

No.

You can’t prove a negative.

There would be no evidence and nothing you can provide to prove it.