This rare kanji has no clear standalone meaning. Treat its meaning as uncertain.
玜 combines 王 (jade/king) and 公 (public), but the exact historical development is uncertain. It may have originally related to a type of jade or a name, but no clear meaning survives in modern use.
The left side 王 suggests jade or a king, and the right side 公 suggests public. Imagine a rare public jade artifact whose purpose is now forgotten, leaving the kanji's meaning uncertain.
For コウ, picture a public (公) jade (王) displayed in a kou (コウ) hall: the kou sound cues コウ while the kanji's shape suggests a public jade.