Knock knock. Who's there? Cows go

Cows go who? No, cows go 'moo'

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? Dough.

Dough who? Dough-n't worry, I knead to come in.

Knock knock. Who's there? Dew.

Dew who? Dew-n't worry, it's just a drop in.