The primary valency of Iron in ${\mathrm{K}}_4\left[\mathrm{Fe}(\mathrm{CN}{)}_6\right]$ is satisfied by

Iron's primary valency in  ${\mathrm{K}}_4\mathrm{Fe}(\mathrm{CN}{)}_6$ is 2. This complex contains  ${\mathrm{Fe}}^{2+}$  in the area of coordination.

Thus, the primary valency of Iron in ${\mathrm{K}}_4\left[\mathrm{Fe}(\mathrm{CN}{)}_6\right]$is fulfilled by 2 ${\mathrm{CN}}^{-}ions$.