!6 across and down (something's wrong!)
16 down: 'Hack a day in Paris operating lifts'
6 letters ??U?N? Possibly relating to lundi or jour. First letter J if 16 across is JUDGEMENT.
But, although I can see the 'gem' in 16 across the rest doesn't make much sense (to me!)
16 across -9 letters - Finding jewel in study during project.