Got a good Knock-Knock joke?

[nanook]

My 4 y/o, the little critic, informed me that mine are not funny. I guess I need some better material . Got a good Knock-Knock joke to share?

 

[Pony]

come look at my question cuz i need some advice!

 

[Amy]

knock knock
who's there
boo
boo who
aw..it's ok dont cry


knock knock
whos there
cows go
cows go who
cows dont go who they go moo

knock knock
whos there
who
who who
is there an owl in here