There are multiple elements that have six valence electrons, including oxygen and sulfur. These elements can be found in the sixteenth group in the vertical column of the periodic table, also known as the chalcogens.
Valence electrons refer to any electrons that an atom contains that are not in a full orbital. Since electrons always fill lower orbitals first, valence electrons are always located on the outer shell. Different elements have different numbers of valence electrons, which affect properties like affinity to bonding. While most elements have some number of valence electrons, elements in the noble gas group consistently have a full outer shell and therefore have zero valence electrons.