Answer
Coordination number: 5
Oxidation number: $+2$
Work Step by Step
The ligand ($CN_{5}$) that surround the central metal atom $Ni$ are 5. Thus, the coordination number is 5.
Let us suppose the oxidation number of $Ni$ is X. To find the oxidation number, we sum the known oxidation numbers and equal it to the charge on the complex.
$CN_{5} = 5\times(-1)$
The overall charge is $-3$ on the complex, thus:
$X + 5\times(-1) = -3$
$ X -5 = -3$
$X =-3+5$
$X= +2$
The oxidation number of Ni is +2.
