Syllable division derived from spelling — this word is not in the pronouncing dictionary, so no phonetic transcription is shown rather than a guessed one.
don't-know is a noun meaning "a person who responds `I don't know' in a public opinion poll". It carries one recorded sense.
a person who responds `I don't know' in a public opinion poll
“70% in favor, 13% opposed and 17% don't-knows”
colloquialism
Definitions, synonyms and semantic relations for don't-know come from Princeton University’s WordNet. Commonness is measured against a corpus of everyday English. Full sources and licences.