Do you know about that is: Sabes de eso
This is how u say it in spanish: que quieres saber?
Translation: Sabes español?
¿Sábes qué? = Do you know what?
¿Me conoces?
i didn't know that you speak spanish = no sabía que hablas español.
Yeah, I do...lol did you mean, How do you say, you know lots of Spanish? If that's the case, then you say,"Sabes mucho español".
how to say,you must know your child's weight or age in spanish.
No sé
Sabe usted.....
" Sabes que"
Ellos saben.
Te conozco