In casual spoken English, people often ask, "Do you know if ___?" to find out the answer to a "Yes" or "No" question. For example:
Do you know if you're having a boy or girl?
Do you know if he's awake?
Answers to "Do you know if...?" can include:
Yes, it is.
Yeah, he is.
No, they're not.
No, I don't think so.
I'm not sure.
No, I don't know.
In formal English for writing and for situations where you don't know people well, you usually use "whether" instead of "if":
Do they know whether the child is a boy or a girl?