Turn light not working - all others are

It could also be a fuse in the truck. Some have different fuses for the trailers right, left, running lights, and brake lights. In other words, more than one fuse.

They do sell testers that plug into the 7 way to help you track it down and or eliminate that as a chance. You can do the same thing using a multimeter.

You might also check the wiring on the truck camper pigtail. It might also not be in all of the way.

Have you checked the trailer plug/connector?
There could be corrosion, or the turn signal wire could have broken or slipped out, on either side of the connection.
You could check with a bulb or a multimeter if +12V reaches the connector.
If none of this helps, something may have come loose internally. I don't know about your camper, but in my 2017 N* Arrow, all electrical connections can easily be accessed under the driver's side overhang/rear wall by removing a couple of screws at the lower edge of the rear wall and pulling a sheetmetal cover. Camper needs to be off truck, though.