calculate cell potential for the voltaic cell where its involving the two cobalt species with Copper
The equation noted corresponds well to that of the first half-cell: on the other hand, the potential indicated is not the good one but just that of the standard potential.
The Nernst relation is written $\ce{E=E^0 +0.06*log \frac{[Co^{3 +}]}{[Co^{2 +}]}}$: the potential therefore depends on the concentrations
You can therefore calculate the potential of this half-cell.
You do the same thing with the second to arrive at its potential: from the 2, you can calculate the potential of the cell