This rare kanji has no clear standalone meaning. Treat its meaning as uncertain.
暭 combines 日 (sun) with 皐, but the exact historical development and original meaning are uncertain.
The sun 日 beside 皐 suggests brightness or dawn, but the actual meaning is unclear.
For コウ, imagine the sun 日 rising over a high 皐 hill, and a rooster crows "ko-ke-kok-kou" to greet the dawn: コウ.