Question

What do we use as a reference point to prove that we are always moving even when we are sitting down

Answer 1

Im not quite sure what you mean but do you mean us or the earth? If you mean us a reference is that our hearts are beating, we are breathing, we (may be) blinking, we are using our brains to do everything, etc.

Answer 2

this is a elementary question? in my opinion we could use stars. as the earth is in constant rotation, therefor we are technically still moving if we are sitting, just like being in a car, if that makes since