Which among the following elements does NOT exhibit -2 oxidation...

The given elements belong to Group 16 of the periodic table.

The tendency to exhibit a $-2$ oxidation state decreases down the group due to an increase in atomic size, a decrease in electronegativity, and an increase in metallic character.

Oxygen, Selenium, and Tellurium are non-metals/metalloids and readily exhibit a $-2$ oxidation state.

Polonium (Po) is a radioactive metal with low electronegativity. Therefore, it hardly exhibits a $-2$ oxidation state. Its common oxidation states are $+2$ and $+4$.

Answer: Po