I have a window in my 'Interpump' pump, it's very obvious, if your not seeing one then you don't have one. As for gearbox, I've not heard of an inspection window being in one. I could be wrong.
You are going to have to either contact who made the gearbox, or read/find the manual and see what they say to put in it.
You could also tell us the machine specs and someone might have the same kit to tell you.