If the Nernst equation for the emf of the cell is ${\mathrm{E}}_{\mathrm{cell}}={\mathrm{E}}_{{ }^{\mathrm{cell}}}^0-\frac{2.303\mathrm{RT}}{2\mathrm{F}}{\log }_{10}\frac{\left[{\mathrm{Ni}}^{2+}\right]}{{\left[{\mathrm{Ag}}^{+1}\right]}^2}$ , then the balanced redox reaction involved in the cell reaction is 

$\mathrm{Ni}+2{\mathrm{Ag}}^{+1}\to {\mathrm{Ni}}^{2+}+2\mathrm{Ag}$

The Nernst equation for emf of the cell is given by ${\mathrm{E}}_{\mathrm{cell}}={\mathrm{E}}_{\mathrm{cell}}^0-\frac{2.303\mathrm{RT}}{\mathrm{nF}}{\log }_{10}\mathrm{K}$ where K is the equilibrium constant for the spontaneous redox reaction. The equilibrium constant will be ${\mathrm{K}}_{\mathrm{c}}=\frac{\left[{\mathrm{Ni}}^{2+}\right]}{{\left[{\mathrm{Ag}}^{+1}\right]}^2}$ for $\mathrm{Ni}+2{\mathrm{Ag}}^{+1}\to {\mathrm{Ni}}^{2+}+2\mathrm{Ag}$