This rare kanji has no clear standalone meaning. Treat its meaning as uncertain.
鋧 combines 金 (metal) with 見, but the exact historical development is uncertain. It may have been a phono-semantic compound with 見 contributing the sound, but no clear meaning is recorded.
Since the meaning is unclear, focus on the shape: metal 金 on the left and seeing 見 on the right. Imagine a metal mirror that lets you see yourself, but remember the actual meaning is uncertain.
For ケン, picture a metal can (ケン) being inspected under a magnifying glass (見): can -> ケン, and the metal object is examined closely.