strike, beat, hit
敲 centers on striking something with force: hitting, beating, or knocking against an object.
敲 combines 高 (tall, high) with 攴 (action involving a hand holding a stick), suggesting striking from above or striking something elevated. The exact historical development is uncertain.
The left side 高 suggests something high, and the right side 攴 looks like a hand holding a stick. Imagine striking a high gong with a mallet.
For コウ, picture a kou (こう, a traditional Japanese incense) stick being struck to release its scent: kou -> コウ, and the strike releases the fragrance.