question about "do you know" in a sentence
Who do you know is the richest man in this town?
In this sentence , "do you know" is a parenthesis.

I suppose that "do you know who is the richest man in this town" and "do you know whom the richest man is in this town" are also correct. "Who is the richest man in this town"/"whom the richest man is in this town" is the object of this sentence.

Do you think so? Thank you!

Question

question about "do you know" in a sentence
Who do you know is the richest man in this town?
In this sentence , "do you know" is a parenthesis.

I suppose that "do you know who is the richest man in this town" and "do you know whom the richest man is in this town" are also correct.  "Who is the richest man in this town"/"whom the richest man is in this town" is the object of this sentence.

Do you think so? Thank you!

Answer

do you know is in brackets because it isn't really needed.  After all, you only know what you know.

whom in this position is not correct, but don't worry only about 20% of the English speaking population use it anyway.

Answer

Hello, Lucy,
Thank you for your answer.  I suppose that the following three sentences are all correct and they have the same meaning. Right?
Who do you know is the richest man in this town?
Do you know who is the richest man in this town?
Do you know whom the richest man is in this town?

Answer

Hi Samya, an easy way to remember if you should you WHO or WHOM is to ask yourself the following question: If you can substitute WHO with he/she use WHO or if you can substitute him/her use WHOM

I hope that answers your question. best Lucy