In the plane zip fly there isa GPS, but I know it should be used as a reference only in the flight test.
I was joking about iPads which is what the previous poster was talking about. Handheld GPS units aren't certified and therefore are considered to only be for "situational awareness" but that is no reason not to use every piece of information you have available to you in the cockpit.
There are panel "mounts" for non-certified handheld GPS units, but they're not as common as certified installations in certified aircraft.
It sounds like you're talking about something installed in the panel. If it's installed in the panel, it's likely to be certified and usable for whatever the manual says it's usable for, as long as the installation was also certified. You need to study your aircraft's POH air AFM and addendums added if the avionics have been updated from what was installed when the aircraft left the factory.
Talk to your instructor about it. I'm surprised they haven't discussed it with you already if you're already training. You need to know what avionics are on board and what they're certified to do.
If it's in the panel, it's fair game for an examiner to ask you to show them how you would operate it, if it isn't inoperative (and legally placarded).
If you're taking about an IFR checkride, expect every instrument in the panel to be tested. Even an old ADF. They've recently stopped testing ADF on the written tests, but I haven't seen any guidance to stop testing it on flight tests.
I could be uninformed on that ADF flight test part, but typing this from a grocery store parking lot, I'm not going to look it up here. You can. You'll need to know it more than I will, and it's your job as PIC to be prepared!