I am trying to take the family name "Cohen" back to its root "Caoin." My problem is that no one who is alive knows how it was originally pronounced, and I can't seem to get a consensus from other sites, where I have been alternately told the pronunciation is "KEE-in," "KEEN" and "QU-een" / "qu-EEN" / "QUEEN." Your help is greatly appreciated.

Hello David,
Are you sure about that origin "Caoin"?
According to Edward MacLysacht, in his book, "The Surnames of Ireland", the name 'Cohen' is a synonym of the names 'Coyne' and 'Kyne' in Connacht and occasionally of 'Cowan' in Co. Down.
"Coyne" comes from Ó Cadhain (cadhan, wild goose). And the pronunciation of the vowel would be between 'Coyne' and 'Kyne'.
"Cowan" comes from Ó Comhdhain. And would be pronounced as 'Cow (the animal) uhn'.
-Maidhc.

I knew several Irish people named Coen, pronounced Cone

Coen is also a synonym originating from Ó Cadhain.
-Maidhc.