Which type of electron occupies the outermost energy level or shell of an atom?

Valence electron.

Explanation:

The various electrons of an atom are simply classified in 2 types.

They are known as:

Valence electron Core electron

Valence electron has the property to hold the outermost shell and carries higher energy level of an atom and the core electron are the type of electron which holds the innermost shell and carries the lowest energy level of an atom.