  In a fully-gapped superconductor the electronic Raman response has a
pair-breaking peak at twice the superconducting gap $\Delta$, if the Bogoliubov
excitations are uncorrelated. Motivated by the iron based superconductors, we
study how this peak is modified if the superconducting phase hosts a
nematic-structural quantum critical point. We show that, upon approaching this
point by tuning, e.g., doping, the growth of nematic correlations between the
quasiparticles transforms the pair-breaking peak into a nematic resonance. The
mode energy is below 2$\Delta$, and stays finite at the quantum critical point,
where its spectral weight is sharply enhanced. The latter is consistent with
recent experiments on electron-doped iron based superconductors and provides
direct evidence of nematic correlations in their superconducting phases.
