he's knocking on the door because he lost his key (loste qui)
loste qui? sounds like "lost key". Oui - yes!
they lost their key so they have to knock on the door!
don't worry, I don't understand it either...AND I speak French semi-fluently!
Why don't you get that? It's hilarious!
I think it's supposed to go
Frappe frappe. Qui est la? Liste. Liste oui? Oui!
Looks like a knock knock joke to me
Knock knock. Who's there? Loste. ... Loste who? Yes