Assuming that your leisure battery is fully charged and the caravan 12v electrics were switched on the first thing to check will be the fuse which will either be of the spade type or a glass fuse.
Take out the toilet holding tank and it will be inside the compartment, it might show up better on this
Wiring Diagram
If the fuse is ok use a 12v tester or a multi meter to check for power across the fuse terminals.
If there is no power you need to trace the wiring back, there might be a switch located somewhere or the toilet might be wired through another 12v appliance which needs to be switched on to provide power.
Tracing the wiring back should lead to the fuse board, don't forget to make sure that the 12v power is on.