This rare kanji has no clear standalone meaning. Treat its meaning as uncertain.
哠 combines 口 (mouth) with 告 (announce, tell), suggesting a meaning related to speaking or chattering, but the exact historical development is uncertain.
A mouth 口 beside 告 (announce) suggests someone chattering or talking incessantly.
For コウ, imagine a person chattering so much they sound like a cooing pigeon: coo -> コウ.