Where is the electric potential highest on a parallel-plate capacitor?

So highest potential of a capacitor plate system is on positive charge plate

Explanation:

As we know that capacitor is a device which is used to store electric field energy between its two plates

So here we can say that in order to store electric field energy the two plates of capacitor will hold some charge on it.

Charge on two plates will be equal in magnitude but opposite in sign

So the plate with negative charge will be at lower potential while the plate with positive charge will be at higher potential.

So highest potential of a capacitor plate system is on positive charge plate