I do periodically clean the lens on rear view camera & Skoda state there is a washer cleaner, but how do you [2 person] check if/when the washer operates ? also I do presume the fluid comes from the same container as the screen washers ? & that that the camera lens is glass & not plastic ? 

You don’t need 2 people to check the operation, select reverse operate rear window washer and you’ll see lens being washed on screen.

Thanks Kenny R just tried that & YES that does indeed work !!!