I'm going to assume that this creator is not omnipotent. He/she/zhi/they/it built the world and exist in it but cannot just do any old magic in the world without breaking it. If they can do anything, they just change your mind so you believe.
So this person wants to prove zhi is the creator? First, as a creator, they probably embedded proof in the universe at the beginning, like, "You see the moon? Connect the dots between all the solar system moons every 10,000 years... it spells my name in English. Every 1000 years, they line up for my name in a different language." Or "yeah, I wrote my life story in the DNA of catfish. Go ahead... I'll wait while you translate."
If zhi didn't plan ahead like that, zhi should be able to give you EXACT values for the 19 fundamental unitless constants that make up our universe. We have approximations for them (example: go to Wikipedia for "fine structure constant"). But if someone told us the exact values zhi used, we could test that in physics and verify the results. That would be pretty strong evidence that this person knew their own work, since deriving those values experimentally is beyond our tech (and possibly permanently beyond our tech except by guess-and-check and there are more combinations than we could ever check in the lifetime of the universe).