Knock, knock

The sound of striking a hard surface (twice, two times). Commonly on someone's door (literally). Figuratively there are numerous jokes in English starting with these words. Figuratively one might say "Knock, knock. Who's there? Boo. Boo - who? The reply would be "Why are you so sad?" :)
Call and response is used both in this joking matter and in more serious matters that are wanting a reply.

Toc toc

Dźwięk uderzenia w twardą powierzchnię, zazwyczaj w czyjeś drzwi. Pojawiają się również dowcipy typu "Puk, puk? Kto tam? Hipopotam"

Kuc, kuc