Khadkaana [also spelled as khadkana, kharkaana] is a Hindi/ Urdu word that is used for knocking, in a little informal way. The formal word for a knock is dastak, and hence formally knocking is called dastak dena.
However, khadkaana can be used not only for knocking but related acts or noises as well. For example, doors or windows hitting the frame or wall and the sound produced thereof can be called khadakna too. When windows make a noise due to wind, that again is known as khadakna.
In Comedy Nights with Kapil, Navjot Singh Siddhu usually says 'khadka do' or 'Khadkaao' for jokes or songs, which would loosely translate to 'knock it' or 'move it', which simply means that you can speak, or sing, as be the case. Still, it's an unusual usage for the word, probably never seen before in Hindi at least.