How can I tell if the problem I have is with the master or slave clutch cylinder? 2008 VW Eos

How can I tell if the issue is with a clutch or a slave master cylinder as symptoms are relatively the same. My clutch will not pop back up. I cannot change the gears while the engine is on. I can change the gears when the engine is off. I do not know which service to select.

My car has 98200 miles.
My car has a manual transmission.

– How can I tell if the problem I have is with the master or slave clutch cylinder? 2008 VW Eos