Knock knock. Who's there? Egg

Egg who? Egg-cuse me, I'm cracking under the pressure to make a good pun.

Knock knock. Who's there? Flour.

Flour who? I knead you to let me in, it's a loaf-ing matter.

Knock knock. Who's there? Cows go

Cows go who? No, cows go 'moo'

Knock knock. Who's there? Brew.

Brew who? Tea-rific to meet you.