How do you know he can't come?

怎么见得他来不了？

《新英汉大辞典》

How do you know he asked me out?

你怎么知道他约我出去？

youdao

Because he was crazy. How do you know he was crazy?

因为他疯了，你怎么知道他疯了呢？

youdao

He told the president, "You do not know the dishonest purposes of those men as well as I do."

VOA: special.2009.08.13

You know he's willing to do anything to win the new administration's support, to listen to him and accommodate him."

VOA: standard.2009.03.18

' Well, how do you know he's terrific?

WSJ: The Weekend Interview with Leslie Michelson: Doctor to the 1% (and Maybe Someday to You)

You go in there and you know you can do it because you know he's behind you.

CNN: Charlotte Dujardin: 'The girl with the dancing horse'

"It's nice to know that you won't have a gentleman walking on the floor, and, if you do, you know he's not supposed to be there, " says O'Brien.

FORBES: My Time