Howdy Ride Everything. The previous advice that has been given on an outside switch was given under the impression you had a Suburban brand water heater. Your pics show you have an Atwood brand, which probably has only an INSIDE the RV switch, similar to this one....or could be mounted in a cluster of switches. The lightning bolt indicates the electric heating element side of the heater.
The earlier Atwoods can possibly have an electric switch on the backside of the heater. Yours probably would not have this switch. To gain access to the backside of the heater, you may have go thru a cabinet, remove a false panel, etc from INSIDE the RV to accomplish this. I point this out which will be explained below.
We can hope it's something simple, as in resetting an ECO switch, the circuit breaker to the water heater turned off, the water heater not wired into a power source (we have seen this), loose/disconnected wires at the inside switch, etc.
If for some reason the electric element was turned on, without water being in the heater, it's possible the electric element is burned out, which will require replacement......also done from the backside of the Atwood heater.
The following link is a service manual on Atwoods. Page 14 (not page 13 as that's early models) will show how to troubleshoot the electric heating element not working, as well as how to reset the electric side Energy Cut Off (ECO) switch on the water heater.
Hope this helps and you get it working.