Four people return home from work and walk up the stairs to their own apartments in the same building which person is getting the most gravitational potential energy upon arriving at the door of his or her apartment

The person going to the highest apartment door.

Explanation:

Since gravitational potential energy, U = mgh where h is the height above the ground. The person with the highest gravitational potential energy would be the person going to the highest apartment door if we assume that their masses are the same.