Do the teams know ahead of time which legs are non-elimination?
They’re never told directly. In the first two seasons, however, the teams could guess which legs were non-elimination by the way the last clue was written. In elimination legs, this clue would say something like, “The last team to check in to the pit stop will be eliminated.” But the last clue of non-elimination legs would say nothing about elimination. This changed in third season according to our interview with Zach: “After the 6th leg of the race, which was the final guaranteed elimination leg, all clues said ‘the last team to arrive MAY be eliminated.'” While the “final guaranteed elimination leg” no longer seems to hold, this new clue wording has continued past season three.
