Can aromatic rings be cyanated using cyanide as a nucleophile?
Chlorobenzene is generally inert to nucleophilic substitution. It was observed by Rosenmund and Braun that using an ethanolic solution of potassium cyanide and cuprous cyanide as catalyst at 200°C, chlorobenzene converts to benzoic acid. But if the ethanol-cyanide solvent is removed and temperature is raised, then the reaction proceeds to form cyanobenzene. Yield was further improved when ionic liquids like DMF was used. This is Rosenmund-Braun reaction.

Note: Working with cyanide is highly dangerous. Do not handle cyanide until and unless you are a professional chemist.

Reference


Wikipedia: Rosenmund-von Braun reaction
Will cyanide substitute bromine in bromobenzene?
Potassium ferrocyanide, $\ce{K4[Fe(CN)6]}$ can be used as a non-toxic source for cyanation.
There are loads of other catalyst for cyanation like $\ce{ZnCl2}$, palladium or nickel salts.[@Waylander]