A parallel plate capacitor stores a charge Q at a voltage V. Suppose the area of the parallel plate capacitor and the distance between the plates are each doubled then which is the quantity that will change?

The capacitance of the parallel plate capacitor is given by

Capacitance =(permitivity of free space)*(area/distance)

or, C=E*(A/d)

So, if you double both area and distance at the same time, it does not matter.

C=E*(2A/2d)

Here, 2 cancels and we get the same formula

But if you double the area only, the capacitance will double and if you double the distance between the plates, the capacitance will be half.