Answer
Coordinartion number: 6
Oxidation number: +3
Work Step by Step
The ligand $(C_{2}O_{4})_{3}$ that surround the central metal atom $V$ are 3, but since $(C_{2}O_{4})_{3}$ is a bidentate ligand, the coordination number is 6. ($3 \times 2 =6$)
Let us suppose the oxidation number of $V$ is X. To find the oxidation number, we sum the known oxidation numbers and equal it to the charge on the complex.
Also,
$(C_{2}O_{4})_{3}= 3 \times (-2)$
$K_{3} = 3\times(+1)$
The overall charge is zero on the complex, thus:
$3\times (+1) +X + 3 \times (-2)= 0 $
$+3+X-6=0$
$X=+6-3$
$X=+3$
The oxidation number of $V$ is +3