The temp sensor is a thermocouple, i.e. two different bits of metal stuck together. It looks like basically nothing - a couple little wires come together in a blob.
It will be the one that goes to the potentiometer. To see if it's OK, measure the continuity of the whole sensor-and-leads - it should be basically short-circuited, i.e. under 1 ohm. If the sensor shows an open circuit at the board end, it's broken. You will need to disconnect one lead from the board first so that you're not measuring other impedances in the board.