To get the net Ionic equation we must get rid of spectator ions, I.E. the ions that repeat on either side of the equation.
So...!
[tex]Ni_{2}[/tex][tex](aq)^{+}[/tex] + [tex]SO_{4}(aq)^2-[/tex] + [tex]2Na(aq)^+[/tex] + [tex]S_{2} (aq)^{2} -[/tex] → [tex]2NiS(s)[/tex] + [tex]2Na(aq)^{+}[/tex] + [tex]SO_{4}(aq)^{2-}[/tex]
This becomes the following net ionic.
[tex]Ni_{2}[/tex][tex](aq)^{+}[/tex] + [tex]S_{2} (aq)^{2} -[/tex] → [tex]2NiS(s)[/tex]
