Answer:
Well, potential energy is commonly gravitational. Gravitational Potential Energy (GPE) can be given by selecting a reference point (usually the ground) and the position of the object (ball). Measure GPE by GPE=mgh (m is mass of the ball, g is gravity, 9.8, and h is height between two points.) Note: if reference point is below the ball, it will be positive GPE, and if above, negative GPE; energy is measured in joules (J).
Example
If the ball weighs 1 kg, gravity is 9.8, and height off the ground is 1 m, the ball's potential energy is 1*9.8*1 = 9.8 joules