Hey, here's a list (not sure when it was last updated but pretty sure it's current) of the farmable items that can upgrade.
https://xpoff.com/threads/19-quick-start-gearing-guide-bfa.79275/page-8#post-1154004
Chops' video pretty much explains everything by a little TL
R All quest items that reward green (uncommon) value gear have a chance to upgrade to either a Blue (rare) or purple (epic).
The items on the link are the items that upgrade from drops - Not all drops can upgrade.
You can check on the wow website and it will tell you if an item can upgrade (there may be an easier way to check):
View attachment 11866
Items that upgrade to epic are 12 ilevels above your average green ilvl .
So at level 20 an epic upgrade always gives you a 32 ilvl item.
JWL listed every item that can upgrade that also has a secondary stat:
https://xpoff.com/threads/quest-gear-depository-1-60.88692/
good luck!