Work it out - the solution

It doesn't matter which robot you ask the question of - what matters is the question, which is "If I asked the other robot which the door to freedom is, what would his answer be?" Now think about that - if you're asking the truth-telling robot, then the other robot is bound to lie and would indicate the door to death, and the truth-telling robot would report this truthfully. If you're asking the robot who tells lies, then the other robot (the truth-teller) would indicate the door to freedom, and the lying robot would tell you the opposite. So whichever robot you are asking the question of will reply by indicating to the door to death. You just go out the other door.