Answer:
At the top
Step-by-step explanation:
The gravitational potential energy of the box is given by:

where
m is the mass of the box
g is the gravitational acceleration
h is the height of the box above the ground
As we can see, the potential energy of the box is directly proportional to the height above the ground, h. Therefore, the box will have its maximum potential energy when h is maximum, which means when the box is at the top of the ramp.