Puzzles/Logic puzzles/Getting out of Prison 2/Solution
"If I were to ask you which door leads to freedom, which door would you tell me?" If the guard is the liar, then he would have lied and told you the wrong door, but is now lying and telling you that he would have told you the correct door. If he is a truth-teller, he is telling you truthfully that he would have told you the correct door. Either way, whichever door the guard points to leads to freedom.
(A simple solution may be to ask any guard to point out the door he guards.....anyone will point to freedom door only)