jade like stone
琭 refers to a type of stone that resembles jade, a semi-precious gem-like material.
琭 combines 王 (jewel) with 录, which likely contributes the sound. The character was created to name a specific jade-like stone.
The left side 王 (jewel) tells you it's a precious stone, and the right side 录 looks like a carved record. Imagine a stone that looks like jade, recorded in a catalog of gems.
For コク, picture a jade-like stone shaped like a small block: block -> コク, and the stone is a block of jade-like material.