"As you know, my brother cannot read."
Translation:Как вы знаете, мой брат не умеет читать.
Russian is only partially pro drop language. Unlike English it allows for dropping pronouns, but unlike languages like Italian or Spanish it doesn't like to do so most of the time.
Without pronouns sentences often sound curt, awkward and sometimes can even come off as rude, like an order. However, Russian also dislikes repeating words. So if a pronoun has been used once, it can be omitted in the next sentence or several. There are no definitive rules for that, though; it's mostly intuitive.
"Как знаете"/"как знаешь" is an idiomatic expression. It means something like "It's up to you" or "you know better, I guess" with a strong "whatever" tint to it. Like, when you tried to talk them out of something, but now are giving up.
That's why it's a bit jarring when it's used as a straightforward "as you know" and it's better not to omit the pronoun in this case.
"Умеет" has more of a sense of "he knows how to", whereas "может" is more "he is able to". If the doesn't know how to read, he doesn't recognize words and letters. Maybe you've taken away his book or he should be doing his math homework, then he isn't able/allowed to read.