The Germanic substrate - knives?

[Anthony Appleyard]

People have connected Germanic "knife" with various Greek and other words
starting with "kn-", e.g. Greek {knao:} = "scrape". But surely PIE {kn-} would
become Common Germanic {hn-}? Perhaps when metalworking and how to make copper
or bronze came to the Germanic speakers, some time after the PIE -> Germanic
consonant shifts happened, it brought with it an IE but not Germanic word
which got into Germanic with the meaning "metal knife".