A positive charge +q is brought closer to a negative charge -Q. As the charge +q gets closer ti the charge -Q, will the electric potential energy increase or decrease?
Potential energy will decrease.
Gravity and electric force are two forces that can create potential energy. In this way, they are quite similar. In the case of gravity, when two masses are attracting each other, and are allowed to move closer together, potential energy will decrease. When we try to separate two masses, we do work that will increase the potential energy. An example of this would be when a person climbs a flight of stairs.
The situation is the same with electric force. When two attracting charges are brought closer together, potential energy decreases.
It is when we move attracting charges apart from one another that the work we must do against the attractive force causes an increase in potential energy.