Answer by Professional Japanese Teacher
Donata desu ka
Who is it? (more polite)
Dare desu ka
Who is it?
The word for “who” in Japanese is 誰(だれ) dare. Since someone is at your door, we usually use the polite version どなた donata to show respect to the other person.
You can combine this word with desu ka to turn it into a question. If you are just wondering to yourself who is at the door, you can simply say “誰(だれ) Dare?” with a raising intonation.