Take and post a macro photo of the corner of the screen with very good light (and possibly use a prop to keep the camera still) and you might not need a magnifying glass to show if the cover was removed by someone when you didn’t realize it.
If you’re sure it’s on and cant make a purchase, I suppose you would want to use a copper wire or nail that you know is less hard than the glass and try to scratch the screen in a corner area to deform the protector material. There’s no way the cover and adhesive are going to be harder than glass. And if you’re wrong, you’re not super likely to damage the glass trying to locate a cover someone else might have removed for you already.
If you don’t mind a minor scratch, you could use a knife or razor blade to score enough of the corner to get the cover off or make a lip you could then slip the blade under. I don’t recommend that and let the cover wear or just pay for a replacement screen when yours no longer makes you happy. I worry if your screen has adhesive, and is that bonded, you might not like the glass or be able to clean the residue unless you know from the manufacturer what chemical will remove the adhesive and not damage the glass or the coating on the iPad.