Answer
Coordination number: 6
Work Step by Step
The metal $Co$ is bonded to two ligands, $(C_{2}O_{4})_{2}$ and $Cl_{2}$. Oxalate $(C_{2}O_{4})_{2}$ is a bidentate ligand whereas Chloride ($Cl_{2}$) is a modentate ligand. Two oxalate are present ($2\times2=4$) and two chloride are present $(2$).
Thus, the coordination number is $4+2=6$
