Julia threw a baseball straight up into the air. according to the law of conservation pf energy, when isthe total potential energy of the ball greatest

The potential energy can be calculated using the following rule (when thrown straight upwards with no angle):
potential energy = mgh 
where:
m is the mass
g is the acceleration due to gravity
h is the height

Based on the above rule, the potential energy of the ball will be highest at the highest point the ball reaches before it starts falling back.