Chelonians do tell people apart, and they prefer some people over others. I noticed to my surprise, that there are people my friendly snake does not like for no reason I can make out. He'll sit there for up to 15 minutes. In general, you can't potty train the animal. It will train you.
Many reptiles follow a daily routine which also includes eliminating.
Many reptiles also show a strong preference for eliminating into their water dishes. The more the better, but not so much that the animal does not get to sleep or eat. Especially new animals should be left alone for the first few days or weeks, until they develop a rhythm and eat well. Then handle for a short time maybe twice a day. Watch the animal.