If an atom has lost or gained electrons, would the charge of the ion go in the lower left or the upper right?

upper right.

Explanation:

when an atom lose or gain any electron it's charge will changed and it will show on the upper right side of the atom symbol.

If atom lose any electron so positive sign shows along with the number of electrons lose.

and if atom gains any electron negative sign will show on upper right side of the atom symbol along with the number of electrons gained.

upper right