What is the electron configuration for $S^{2-}$ ion?

Explanation:
A good starting point when looking for the electron configuration of an ion is the electron configuration of the neutral atom.
In your case, the neutral atom is sulfur, $S$, which is located in period 3, group 16 of the periodic table. Sulfur's has an atomic number equal to 16 , which means that a neutral sulfur atom has a total of 16 electrons surrounding its nucleus.
The electron configuration of a neutral sulfur atom will thus be
S: $1s^{2}2s^{2}2p^{6}3s^{2}3p^4$
Now, the sulfide anion, ${\mathrm{S}}^{2-}$, is formed when two electrons are added to a neutral sulfur atom.
As you can see in the configuration of the neutral atom, these two electrons will be added to the 3 p-orbitals, which can hold a maximum of six electrons between them.
The electron configuration of the sulfide anion will thus be
${\mathrm{S}}^{2-}:1s^{2}2s^{2}2p^{6}3s^{2}3p^6$
The noble gas shorthand notation for the sulfide anion will use the electron configuration of neon, the noble gas that comes immediately before sulfur in the periodic table.
${\mathrm{S}}^{2-}:[\mathrm{Ne}]3s^{2}3p^6$