What element has a total of 3 p-sublevel electrons?

N, P, As, Sb, and Bi

Elements with three p-electrons ...

That would be N, P, As, Sb, and Bi - - elements in group 15

For example, energy diagram showing "empty" orbitals up through the 3p.

... 3p __ __ __

3s __

... 2p __ __ __

2s __

1s __

Energy diagram of phosphorous showing three unpaired electrons in 3p-sublevel

... 3p ↑_ ↑_ ↑_

3s ↑↓

... 2p ↑↓ ↑↓ ↑↓

2s ↑↓

1s ↑↓

According to Hund's rule, the electrons singly occupy the p-orbitals, and all have the same spin.