What kind of dimmer is it?
a) Capacitive Sensorb) Pressure Sensorc) Something else (specify)
How do capacitive sensors work
No idea from that blurry photo.
How do you interact with it.
By sensing capacitance between the plate and ground as your body affects it.
If you don't maximize the photo, it will be easier to see
Would the "ground" be "the Earth" in this case?
In Arduino, capacitive sensing only works when you connect it to the Earth somehow
The pad seems to be made of metal
I have a similar dimmer with a plastic coating.