You should be able to feel it easily through the carpet as the plate sits on top of the tunnel and has a raised bulge upwards just in from the edge. Presumably the carpet has been glued down so you can't just lift and look.
Prop shaft may or may not have grease nipples in the universal joints at front and back. Greased from under the car.
Do you really mean the access to the front of the " torque tube" which houses the pinion and needs access to grease the front bearing of the pinion shaft?? Have a look at the A7 clubs association archives for the illustrated spares books showing relevant bits.