Well personally I've always been on the fence (so to speak) about whether omnipotent beings exist. I do believe that there are things and beings beyond our understanding and I also firmly believe that there are some things we should not understand but neither of these believes negate the possibility of their being held in error. The question is whether there is a way for an omnipotent being to prove they are in fact omnipotent. Well I must first point that cultures at different stages of development have reacted differently to other cultures at other stages of development. For example when Europeans made their first widely known voyages to "the New World" (which for arguments sake let’s say was Christopher Columbus as most of the public believes) they had reached a point of long-haul oceanic transportation, governmental systems, and various other technologies the Native Americans had yet to achieve. But the Native Americans had also managed to settle a vast landscape ranging from the Atlantic plains and forests to the deserts and scrubland of the Pacific coast. The Europeans had firearms and (infinitely more lethal and almost entirely unknown to them) carried diseases the Native Americans were, at the time, utterly unprepared to face. The Europeans could perform feats the Native Americans could barely comprehend and vice versa (the latter would something the Pilgrims would later be presented with in an act little short of deliverance). By the same token to prove their omnipotence such a being would need to perform feats the person they are being asked to prove themselves to would be able to understand only as the work of an omnipotent being. For example the being might prove their power by compressing a boulder 20 meters across down to the size of a sugar cube and then moving said cube to prove the demonstration. They might make it snow as proof to someone who inhabits an equatorial region. They might make a tree grow if they were convincing a desert dweller. All would be feats that would be beyond the capacity of reason to explain and thus would be demonstrative of the being’s omnipotence. If the person was convinced then their reaction could any number of things. They could worship the being in question (just as many “primitive cultures” have come to revere more advantaged ones in ages past). They could ask/beg to serve them and thus begin proselytizing a new faith or religion on behalf of the being in question. They might be so overwhelmed they lose their sanity and/or grip on reality at large. Or they might follow any of a near infinite number of other paths thereafter. But one thing would remain constant in nearly all scenarios. They would be virtually unable to forget the marvel they bore witness to. They might even attempt to reproduce it themselves in years to come.