"know" for a question, "knows" for a statement. AFAIK, no/any/everyone and no/any/everybody are interchangeable although I prefer anyone.

Does anyone know what happened?
Anyone knows that.

Does everyone know what happened?
Everyone knows that.

Does no one know what happened?
No one knows what happend.

>Hi everybody,
>
>I'm just curious, what would be correct from the English grammar point of view question:
>
>"Does anybody know what happened...?"
>
>"Anybody knows what happened...?"
>
>"Anybody know what happened...?"
>
>"Anybody, what's up with ...?"
>
>Or you can suggest a better form?
>
>Thanks in advance.
>
>And I'd like to know the rules of singular/plural in appliance to
>
>everybody
>nobody
>anybody
>anyone
>everyone