is the rv new to you?.... specifically, have you ever seen that light work?
is the light fixture mounted in to the surface, or does it have a bracket that allows it to swivel? the ones that swivel can be turned enough to pull/break the wires loose..... the ones that are solid mounted usually dont have issues, but it wouldnt hurt to remove it and see if a wire came loose...
if the rv is new to you, are you sure you are flipping the correct switch to turn it on?...... have you swapped out the bulb from one of the other working fixtures to see if makes any difference.....
once we pinpoint the problem, the fix will probably be simple.....