Mandy adn I are of the same line (her grandmother and my grandfather were brother and sister), but our line pronounces it Dun-gun, but our neighbors invariably call us Dun-a-gan
Pronounciation isn't the only problem! U.S. lines vary widely in spelling: Dongan, Dungans, Dangans, Duggan, Dunagan, Dunigan, Dunnigan, Dunkin, Dunkins, Dunikan, and even Dunzann in early records and current lines--all documented as the same families!!! Spelling often varies from father to son and brother to brother prior to 1920 or from one document to another for the same individual. I even have two documents from the mid-1880's (wills) where the spelling varied within the document!