Where can you find all of it? Is it worth completing the quest?

you find it in the forts

there's 1 or 2 in the fort near Hackdirt (begins with a C, Carmala or something. They may even respawn.

I forget what the reward is; nothing impressive like an echanted anything that's for sure.

This is just a little side quest, no time limit and not important. Just collect the bottlrd you find them and give them to her or not. I think I have about 12.

The slaughterfish quest from the guy outside the inn gives you a water breathing enchanted whatsit which is actually useful.

ok thnx man.

List of forts that contain one or more bottles of Shadowbanish Wine: Aurus, Carmala, Dirich, Grief, Irony, Magia, Scinia, Vlastarus.

I also found some in the newest official mod, "Fighters Stronghold".

I finished this quest recently and it's not really worth it IMO. I basically finished it to get it off my Current Quests list.
I believe you get about 500g for the entire thing..maybe a tad more, but it's not much.
She offers about 50gp for each additional bottle you bring her once the quest is completed also.
My character has about 75,000 gp, so I really don't need it.

u know that slaughterfish quest what inn u start it at?!?!?!
ive been dying to do that quest is it 1 with the giant slaughter fish???

The Wawnet Inn just outside Imperial City.
There's some guy outside on the road.

The giant slaughterfish I ran into is in one of the Thieve's Guild quests.