${\mathrm{E}}_{{\mathrm{Ni}}^{+2}/\mathrm{Ni}}^0=-0.25\mathrm{V};{\mathrm{E}}_{\mathrm{Pt},\frac{1}{2}{\mathrm{Cl}}_2/{\mathrm{Cl}}^{-}}^0=+1.36\mathrm{V}$     then the spontaneous reaction involves

SRP of Nickel electrode is less .. It acts like anode
SRP of Chlorine electrode is high.. It acts like cathode
$\begin{array}{l}\therefore \mathrm{At}\mathrm{anode}\mathrm{Ni}\left(\mathrm{s}\right)\to {\mathrm{Ni}}^{+2}\left(\mathrm{aq}\right)+2{\mathrm{e}}^{-}\\ \mathrm{At}\mathrm{cathode}{\mathrm{Cl}}_2\left(\mathrm{g}\right)+2{\mathrm{e}}^{-}\to 2{\mathrm{Cl}}^{-}\left(\mathrm{aq}\right)\\ \mathrm{Ni}\left(\mathrm{s}\right)+{\mathrm{Cl}}_2\left(\mathrm{g}\right)\to {\mathrm{Ni}}^{+2}\left(\mathrm{aq}\right)+2{\mathrm{Cl}}^{-}\left(\mathrm{aq}\right)\end{array}$