In Doomwood, or you could just travel to Necropolis/Doomwood via the Gryphon (Click the sign next to Ash and then Travel)
Yes, you need to do all of the necropolis quests except Extra Credit
You have to go to Artix in necropolis and the go to one of his quests called haunted castle and when you finish the quest it will give you 1 unlucky doom essence.
Artix @ necropolis
Artix is found in The Necropolis
there is no set amounrt of quests in dragonfable because the creators are constantly updating and adding new ones
In quests
From Yuglars Quests
To invite Artix on Dragonfable, all you have to do is go to Necropolis, talk to him, select invite, and pick friend A or B.
finish artix's quests in the nectopolis
Complete Valencia's quests.
Go to Necropolis, talk to Artix, and do the haunted castle quest
Talk to Ash in Dragonfable and go to Quests. You need to click Challenge, that will take you there.