First pull the lenses and check the bulbs. If they are OK then you probably would need to unscrew the fixture and check the wires coming to the fixture. If they look secure then take a multimeter or a test light and see if you have power to the fixture. If you don't have juice to the fixture, chances are you have a cut wire between the fixture and the panel or maybe that fixture wasn't hooked up originally.
2016 Ford F150 Platinum
2013 Coachmen Freedom Express 233RBS
Prior: Jayco Pop Up, Shasta Bunkhouse, Rockwood 2560G Pop Up