• Who knocks at the door?

  • Who does knock at the door?

I am confused here. Usually, first sentence is acceptable. But I did not read about the 2nd one. Is it correct? Is it an emphatic sentence of present indefinite tense?

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    It is preferable that you pick one site to post your questions on rather than posting them on multiple sites. – Catija Jul 23 '15 at 8:06
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    We understand your dedication to your students, but still stack exchange has rules, stated in the help centre and discussed in meta - so what Catija had said is for the benefit of other users of the website(s). If someone else comes along with a similar question it will be easier for them to find answers in one answer thread, instead of hunting for it across stackexchange :-). (An aside, all comments you leave under Khans answer actually ping Khan, so it is better to leave general comments that don't refer to that answer directly underneath the question). – Lucky Jul 23 '15 at 17:32

Who knocks on/at the door?

Who does knock on/at the door?

The first sentence is grammatically correct, whereas the second is incorrect.

When you start a sentence with the pronoun "who" as the subject in a sentence, you don't need to use the auxiliary "do/does/did". On the other hand, when you use who as the object at the start of a sentence, you need to put this auxiliary after it in front of the subject. For example:

Who do you want to talk to?

who did you meet?

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    To add to Kahn's answer, I would usually see: "Who is knocking on the door?" or "Who is at he door?" Although the constructions you have provided are correct. – SolarLunix Jul 23 '15 at 8:06
  • Catija:What I can do? I share my posts .but I don't get comments. That's why I share my posts on different sites so that I may get quick response. My some posts are not fully answered. I requested our teachers for solving them. – I don't know who I am. Jul 23 '15 at 8:16
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    @user124234 you need to be more patient. You can't expect an answer in five minutes, and you shouldn't accept an answer you get that quickly. You need to be able to wait at least a day for people to really answer your questions. – Catija Jul 23 '15 at 8:31
  • Okay, Catija.but l also have to tell these things to my students. That's why I can't wait. But now , as you said. I will have to wait for your answers. – I don't know who I am. Jul 23 '15 at 8:47

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