Besides Halloween, today is also national Knock Knock joke day-

http://nationaldaycalendar.com/national-knock-knock-joke-day-october-31/

Know any good ones? Ok, there are no good ones. Know any?

It's my topic and I'm giving it a reply before the day ends. I I'll keep it TV related.

Knock, Knock!
Who's there?
Doctor.
Doctor who?
That's a great T.V. show, isn't it?