Question

What bosses/mobs drops the gems for the new Gem Atelier?

List with type of boss/mobs works perfectly.

Answer 1

For the moment we know 2 bosses that drops gems in the first kill 100%

This bosses are the 2 final bosses of the new quests

Despor - Final boss of the 20 years a cook quest
Mitmah - Final boss of the Adventures of Galthen (Part2)

Remember that this extra loot will only apply in the first kill!

I hope i helped you, 

Gleemody

Answer 2

Every Archfoe Boss with Co-op loot can drop Greater Gems only (any boss which loot comes in an special bag that u can't autoloot), this is confirmed by CM, Every influenced mob can drop lesser/regular gems only (really rare), while Every Fiendish (even trivial) can drop all kind of Gems, and it's also the fastest way to grind gems by far.