Overall reaction?

Ni²⁺(aq) + 2e⁻ → Ni(s) …… E° = -0.28 V
Zn(s) → Zn²⁺(aq) + 2e⁻ …… E° = -(-0.76 V) = +0.76 V

Add the above two half equations, and cancel 2e⁻ on the both sides.
The overall equation is :
Zn(s) + Ni²⁺(aq) → Zn²⁺(aq) + Ni(s) …… E°(cell) = -0.28 + 0.76 V = +0.48 V

One get turned around such that the electrons cancel out. The answer with a positive potential is:

Zn + Ni+2 --> Ni + Zn+2 and the potential is 0.76 - 0.28 V or 0.48