If you have your system set up to have a separate tipping screen (on the app, settings-> tipping, scroll to the bottom), your customer has to tap a tip option before getting to a receipt/signature screen. Without the separate tip screen, yes, your customer can bypass the tips without tapping.

My guess is (and please correct me if I'm wrong) that you're wondering if people are missing the tips at the top of the screen. The easiest way to solve that is to put the separate tip screen into use.

As for your question, I haven't found a report that shows specific taps of tip options. Your daily sales report email will give you your tip percentage over the entire day, but I don't believe there's a way to see who tapped the No Tip button.