<kn->

There are a few English words starting with the letter sequence <kn>:

• knack
• knag
• knap
• knar
• knead
• knee
• kneel
• knife
• knight
• knicker
• knickerbocker
• knob
• knot
•  ...

The <k> is a silent letter in all these words. <kn> had been pronounced /kn/ in Old, Middle and Early Modern English times before it was reduced to /n/ (via /x/ and /h/) in the 16th and 17th centuries.

The only word I'm familiar with which has initial /kn/ is the word 'knesset'. The earliest quotation attested in the OED dates back to 1949. So the word seems to have entered the English language long after the change from /kn/ to /n/ had taken place.
Correction: In the meantime another word with initial /kn/ popped up in my mind: 'Knossos'.
Being a modern loanword, however, does not prevent it from being adapted to the usual sound restrictions:

credit: www.unilever.co.uk

credit:www.knirpsumbrellas.co.uk