If I add a "?" at the end, would it change this to "How do you know?" or do I need another "do" word?
By the inflection. Maybe not with the duobot but when languages are spoken you can usually tell its a question by the way it sounds.
How do you know é uma pergunta: How do you know it?
As you know é igual quando falamos: Então, como você já sabe...
Not really. If you add the "?", then it would only mean "as you know?"
The idea of usig "como você sabe..." is to begin a sentence remarking that the person you are talking to already knows what you are about to say after that. Ex.: Como você sabe, eu falo português e inglês. (As you know, I speak Portuguese and English.)
I wrote "Like you know" and got it wrong :( Not even sure if I should report it as an alternate answer though.
Just my two cents: when I hear someone say, "like you know" it's generally derogatory to the person being addressed. Ex.: "I would do it like this." "Like you know!"
I wrote, "Como vocês sabe" and it marked it wrong, saying it was "Como você sabe". These both sound identical so I know the difference between você and vocês but why wouldn't it accept both answers just for this question?
The plural version is "Como vocês sabe
m?", so that's how you see this is a plural sentence.