If an omnipotent being wants you to believe something that isn't true, and is willing to use its omnipotence to convince you of the truth of that untruth, then there is nothing you can do about it. There is no observation that suffices to prove that an omnipotent being is telling the truth, as a malevolent omnipotence could make you believe literally anything - that you observed any given observation - or didn't, or that impossible things make sense, or sensible things are impossible.

This is one of a larger class of questions where one answer means that you are unable to assume the truth of your own knowledge. There is nothing you can do with any of them except smile at your own limitedness, and make the assumption that the self-defeating answer is wrong.