is this sentence correct? When do we use it?

It's correct. It would be another way to ask "Why do you wear a coat?"
In old-fashioned English it could mean "Why are you putting on your coat now?"

So why do you put on your coat? And why are you putting on your coat are interchangeable?

Not in modern English.

"Why do you put on your coat" is correct, but not often used. I wasn't sure if you were looking at a modern English sentence, or if you were looking at a very old book, so I gave you both possibilities. In today's English they are not the same.

fivejedjonNot in modern English.

Can you explain regarding this, sir? Does the difference lie on the time frame and situations, where "why do you out on..." means something more universal while "why are you putting on..." means that he is currently putting it on and only at that time?

English has changed over the centuries, and there are some ways that people used to say things hundreds of years ago that we do not say today. "Why do you put on your coat" had a slightly different possible meaning hundreds of years ago. It isn't used to mean that now. I didn't know if it was the old meaning you were looking for.

Blue JayEnglish has changed over the centuries, and there are some ways that people used to say things hundreds of years ago that we do not say today. "Why do you put on your coat" had a slightly different possible meaning hundreds of years ago. It isn't used to mean that now. I didn't know if it was the old meaning you were looking for.

I'm looking for the mo

Why do you wear a coat?

JesterLegacyIs this sentence correct? When do we use it? Why do you put on your coat?

It is correct. I take 'you' as impersonal 'you'. Thus to me it means:

Why does a person put on their coat (on all those occasions when he or she puts on his or her coat)?
Or,
Why do people put on their coats?

It expects an an

Yes, this was why I wondered if JesterLegacy was looking at an old text.