Knock-Knock, Who's There?

I guess all pre-schoolers go through a knock-knock joke phase, don't they?  Myrick has been in one for about a year.  Some are funny, many are made up, and we laugh at all of them despite their funniness or not (and many of them are just downright silly).  So having an older sister who never stops regaling you with her endless arsenal of knock-knock jokes makes you think you should get a few, too, doesn't it Pender?  And here we go...