I dont have shower doors where I live now, but I used to use soft scrub on them. I would spray generously, wipe it around all over and let it sit while I clean something else, then scrub and rinse.
If it's hard water stains, vinegar is what works. I didn't have hard water when I had shower doors, but do now, and I have to soak my shower heads in vinegar once every year or two, which completely dissolves the hard water deposits, so I'm thinking if it is hard water deposits staining shower doors, remove them, lay them flat and let vinegar sit on them a good long while. Maybe in a garage or driveway.