You're correct, Bob. A doyna is a generic term for an improvised, free-rhythm solo, which in traditional klezmer bands was usually played by the clarinet. (No doubt some have had words put to them, which may be what Bill H is remembering.) It's often based on a Hasidic nigun, which is a wordless melody that's intended to amplify an intense personal religious experience...or simply to express joy. Not related to "Dona Dona".

Aloha,
Mark