With COMAND NTG 5.5, our 2019 C Class is only pre-MBUX, but you can see the map version in the options. I believe it can be found in the Navigation menu and on the main page of the system settings.
Because of how long it takes for OTA map updates to load, I usually just use Mercedes Me on my computer to download them to an SD card, and then I install them in the car that way. A USB stick might work as well, though I haven't tested that.