2) Knock and knot come from Anglo Saxon language and the k used to be pronounced, but over time, they were dropped. As far as iron, I don’t know about you, but I pronounce the r, and I don’t know of anyone who doesn’t.

PS: I also pronounce the p in humpty and dumpty.

Ok, here’s a serious answer for 1) poultry seller or poultry farmer if it is sold directly from the poultry farm.

You should ask: WHAT do you call…….not how do you call….

There is no explanation because you don’t omit the K in those words. Omit means a different thing, maybe you mean don’t pronounce. K and R in those words as well as the p in empty or humpty dumpty are called voiceless consonants.