Just asking for info really

How does the sensor/valve know what wheel it is on to tell the onboard readout?

If you took one off the the front right and put it on rear left would it just know or mess up with errors or give readings for wrong wheel?

 

The short answer is that when your steering wheel is turned the car knows exactly where it is pointing and when you turn while driving all the wheels travel by a different amount relative to each other, this is constantly measured by the ABS Sensors irrespective of what tyre is on that Hub so the car is clever enough to work out where each wheel is on the car after a short period of time.  

You can move Tyres from front to back but some tyres are Directional so they should not be moved to the other side.

Is that car definitely one where tyre pressure warning is based on relative rotation measured by abs sensors as opposed to transmitters on the bottom of valve stems?

On the Mk7.5, the 2013 and earlier cars didn't use sensors, just the ABS. In 2013 they introduced the TPMS valves. The car has aerials fitted around it to pick up transponder signals from them. Basically, you train the car so it knows which valve is on which wheel. A series of on and of selections on power button or key and it goes into trainbing mode and you use a little box next to the valve as called for on screen. Not sure if the Mk8 is the same though.