The reaction is:
(C₂H₃O₂)²⁻ + NH₄⁺ = (NH₄)(C₂H₃O₂).
and
are the spectator ions.
The reactants in the reaction is sodium acetate and ammonium carbonate. They form the soluble molecule sodium carbonate and slightly soluble ammonium acetate. This is a double displacement reaction.
Spectator ions in the reaction are those ions which are present in the reaction but they actually don't take part in the reaction that's happening and they remain same before and after the reaction. In this reaction, the spectator ions are sodium and carbonate which remain in ionized form in the solution before and after the reaction.