Mk3's with onboard satnav have "Navi" as part of the model name.
To turn the screen off, use the brightness button (contains sun & moon symbols). That should toggle between daytime, nighttime, and off settings. I think that might still leave the clock active on the screen (haven't tested it myself), because you'll lose the one on the right-hand multi-info display when you use cruise control or the speed limiter.