Two protons are brought towards each other. Will die potential energy of the system decrease or increase ? If a proton and an electron be brought nearer, then?

Potential energy will increase. This is because in bringing two protons closer, work has to be done against the force of repulsion. This is stored up in the form of potential energy.
However, the potential energy will decrease when a proton and an electron are brought nearer. Work will be done by the force of attraction between them.