shadow banish wine

Ok, because that is worded very oddly, and it's horribly vague, I'm going to assume your talking about the Shadowbanish wine that creates a quest when you find the first bottle. All the information for completing the quest is in your log, so read it, and head to the city and find the person it's talking about. Simple really.

This is a very rare wine.....it's used for a quest. I suggest not using it for anything except for the quest. Just follow what the log says.

You find them in forts, not every one, but in a few, just look in everything in forts

i for one have completed most of the quests so i just do things randomly one of those random things is wine collecting i do not belive that shadow banish is the rarest wine in the game there is like 13 bottles of it i have only found like 4 fellmoor red wines in the shivering isle and there is varyations of it like felloor swamp wine but in any case it is a cool wine to add to any colletion

There is two bottles of it in the niben bay islands.
But where do I start the quest?

There is 18 shadowbanish wines in total. There are a total of 8 forts 2 of each wines can be found in each fort. Good luck happy hunting