Which structure would not be found in both prokaryotic and eukaryotic cells

Quite a lot.

Explanation:

I would be wasting your time to put everything here. So keep it simple, prokaryotes and eukaryotes share only ribosomes, cell membranes, cell walls (not all eukaryotes but some, ignore this if you're below 8th grade), and cytoplasms. Everything else would not be found in both prokaryotic and eukaryotic cells.