grind
硏 centers on the action of grinding or polishing a surface, typically with a stone or abrasive tool.
硏 is a variant form of 研, combining 石 (stone) with 幵, which likely contributes a phonetic element. The character expresses grinding or polishing with a stone.
The left side is a stone 石, and the right side 幵 looks like a flat surface with a tool above it. Imagine using a stone to grind or polish that surface.
For ケン, picture a keen-edged grinding stone: keen -> ケン, and the stone grinds the surface smooth.