Curiosity-
Thank you.
I already knew the “real” answer, but didn’t want to steal it from someone else who could solve it.
There are two possibilities. Let’s name the two people “X” and “Y” (such imaginative names, I know):
1) Ask X “which door would Y tell me is safe?”, then use the other door. If X is the honest one, he will point to the door that Y (the liar) would have indicated, while if X is the liar, he would dishonestly point to the door Y would not indicate.
2) Ask X “Hypothetically, if I asked you which door was safe, which door would you point to?”, then use the indicated door. If X was the truth-teller, he’d honestly point to the safe door that he’d point to if asked. If X is the liar, he’d dishonestly point to the safe door that he wouldn’t have pointed to if he’d actually (not hypothetically) been asked.