This rare kanji has no clear standalone meaning. Treat its meaning as uncertain.
The exact historical development of 揈 is uncertain. It visually combines 扌 (hand) with 訇, but the original semantic and phonetic roles are unclear.
With no clear meaning, focus on the shape: a hand 扌 beside the complex 訇. Imagine a hand trying to grasp something loud and confusing.
For コウ, picture a hand striking a gong: the sound 'ko' echoes as the hand hits the right side 訇, which looks like a noisy object. Gong -> コウ.