I've got the quest where you need to deliver to somebody in Balmora, but I've talked to everyone and nobody mentions anything. Does anybody know who the person is?

Doesn't the quest give you a name or a specific location, via dialogue or journal entry?

Vorar Helas is the guy your looking for in Balmora.
Be the nice guy instead and take her to the Argonian Mission in Ebonheart.

No, it just tells me "Someone in Balmora"
And Shikishima, looking back at my description of this, I realise it could have been that quest.
To clarify:
I am on a quest from the mod "Vvanderfell Druglord"
I need to deliver 35 vials of Skooma to somebody in Balmora
I have the Skooma
Nobody I talk to says anything about skooma exept the normal "I've herd it makes you..."

I can't recall the names off the top of my head. But there's a basemant in a house owned by a Khajiit. The person you are looking for is in that basemant.