The major product for the following reaction is :

Nucleophilicity of sulfur-containing nucleophiles (such as ${\mathrm{SH}}^{-}$) is higher than that of oxygen-containing nucleophiles (such as ${\mathrm{OH}}^{-}$).  Here Sulphur containing nucleophile can donate its lone pair. A stable carbocation is formed next, stable carbocation will be that which is away from CN group.