This rare kanji has no clear standalone meaning. Treat its meaning as uncertain.
The exact historical development of 勬 is uncertain. It combines 力 (strength) with 絭, but the role of 絭 is unclear.
With 力 (strength) on the right, 勬 might suggest effort or force, but its meaning is not established. Think of it as a mysterious strength-related character.
For ケン, imagine a strong person named Ken using their strength: Ken -> ケン, and the 力 component reinforces the idea of power.