The typical Lewis represention of cyanide anion is as #:N-=C:^-#. Of course this means that nitrogen has an oxidation number of #0#, because the sum of the oxidation numbers must be equal to the charge on the ion. We conceive that the 6 electrons that comprise the carbon nitrogen bond are shared by the participating atoms. And there are this 5 electrons around nitrogen, i.e. a neutral nitrogen, #Z=5#, and 5 electrons around carbon, #Z=4#, an ANIONIC carbon.
Other formalisms are possible. What is the oxidation number of iron here? This is something you will be asked to assess.
If we draw the Lewis structure of cyanide anion as #""^(-):stackrel(ddot)N=C:#, then carbon has an oxidation number of #0#. But I can't think offhand of a complex where cyanide anion binds thru the nitrogen.
