Number of $cisN-Mn-Cl$ , i.e. $Mn-N$  and  $Mn-Cl$ bonds are in adjacent positions

$1-Cl\left(a\right)-Mn-N\left(1\right) 2-Cl\left(a\right)-Mn-N\left(2\right)$

$3-Cl\left(a\right)-Mn-N\left(4\right) 4-Cl\left(b\right)-Mn-N\left(4\right)$

$5-Cl\left(b\right)-Mn-N\left(3\right) 6-Cl\left(b\right)-Mn-N\left(1\right)$

Hence, the answer is 6.
Note:  All Adjacent positions $\left(at90°\right)$  are $cis$  to each other