Hi, best bet is to invest in a repair manual. I just bought a 96 Cab needing a rear window. I saw three top shops, none of whom knew that the window zippers in. It's a rare car.
Coincidentally, I bought the Audi repair manual, published by Bentley (I got mine on EBay for $80, it sells retail from Bentley for $105) and found out that the window zips in, then is glued onto the top using heat sensitive glue that is set by sending current through wires already in place in the convertible top. The manual says you need a special Audi tool that presses the top against the window while the glue is setting, I don't know about that, I haven't had mine done yet, but it looks like a good idea to do it that way to be sure of a watertight seal.
I had to buy the Bentley manual as I couldn't find an aftermarket repair manual on this car from Haynes or Chilton or anyone else. Good luck.