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:

[![enter image description here][1]][1]

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:

[![enter image description here][2]][2]


  [1]: https://i.sstatic.net/j6N7H.png
  [2]: https://i.sstatic.net/Yo9Yu.png