First, since there are no electrophiles that are formed, the only reaction that comes to mind is nucleophilic aromatic substitution.
$\ce{NaOH}$ does a displacement reaction with $\ce{K3Fe(CN)6}$, yielding the $\ce{CN-}$ ion.
The cyanide ion attacks the benzene ring, giving three possible resonance structures:
The hydrogen attached to the carbon with the cyanide ion is accepted by the strong base $\ce{NaOH}$.
Next, the nitrile undergoes acid-catalysed hydrolysis to form a carboxylic acid:
