It's going to be either an Atwood or a Suburban 6 gallon heater. Elements for either one can be purchased online or at a store. You can get the model number from a placard which is located somewhere inside the access panel. Replacing them is easy. Remove element cover, disconnect two wires, use an element wrench to unscrew it, remove, then just install a new one by reversing the process. Depending on the model you may need to remove the
propane burner tube to get access to the element cover. There are plenty of YouTube videos that walk you through the process.
Make sure to disconnect any power, disconnect the water supply, make sure your water pump is off, and drain the water heater before attempting to replace the element.