Answer
The precipitate is CdS.
Na$_{2}$S (qa) + CdSO$_{4}$(aq) -> CdS(s) + Na$_{2}$SO$_{4}$ (aq)
Work Step by Step
Ionic compounds containing sulfide ions are insoluble unless they contain an alkali metal, or a barium, strontium, or calcium ion. Because sulfide reacts with cadmium here, it will form a solid precipitate.
