What are the areas of an aircraft that suffers most from G forces?
Basically 3 places on an airplane see very high concentrations of stress in a small area from in-flight G loads.  In this case we'll say a single engine light aircraft.


Wing root spar fittings on a cantilever wing - the bottom in tension and the top in compression. For a high wing airplane with struts, it will be the strut attachments at each end that join the strut to the fuselage and wing.
The roots of the horizontal tail, same except upside down - bottom in compression and top in tension.
Engine mount attachment to the firewall - top mount in tension and the bottom mount in compression.


Those are the points where flight loads from a lot of mass are concentrated at a single point or set of points during high G loading and are where the structural elements will be heaviest.  For most other areas the loads are distributed over more of a large area.