I don't know means you don't have the answer or the information. In conversation it's also a way to buy time or soften a reply: I don't know, maybe Friday? In fast speech it sounds like dunno, and in texts it turns into idk.
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I don't know + what/where/why/if + subject + verb; I don't know, maybe…; I'm not sure (softer); I have no idea (stronger)
- I don't know what time the shop closes, let me check online.
- — Where should we eat tonight? — I don't know, maybe that new Thai place?
- I don't know if my boss will let me leave early on Friday.
What changed
First versionSorry, I don't know where is the bus station.
RevisionSorry, I don't know where the bus station is.
In a question, the verb comes before the subject: Where is the station? But after I don't know, it's no longer a question, just part of an ordinary sentence, so the order is the usual one: where the station is. Learners often carry the question order over unchanged.
You can say you don't know with different strength. I'm not sure sounds soft, as if you almost know: I'm not sure, maybe Tuesday. I have no idea is stronger and blunter. With strangers and at work, I'm afraid I don't know is a handy choice.
Your turn
I'm new in this town, so I don't know ___.
Show the answer
where the post office is — After I don't know, the question becomes part of the sentence, so the order is the usual one: first the post office, then is. Where is the post office is the word order of a separate question, and here it's no longer a question.
A friend asks what time a concert starts. Write a reply: say you don't know the exact time and suggest where to check.
I don't know what time the concert starts, but we can check the venue's website.
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