"As you know, my brother cannot read."
Translation:Как вы знаете, мой брат не умеет читать.
I got dinged for dropping the pronoun ты, which send to me too be something pretty common, especially when the second person isn't the point of the sentence
You forgot вы and мой. You basically wrote "As know, brother doesn't know how to read".
But this is possible in Russian (as it is also in Spanish for example) - at least sometimes. Only unfortunately I don't know the rules to this, so I would be happy, if some native speaker could explain it in this context.
Even though I am a native speaker, it's hard for me to explain all the rules here, because there no strict rules. But often leaving the pronoun out feels unnatural even if it's obvious from the context. Bettyru2 explained it pretty well.
I just wanted to add, that "как знаете" or как знаешь" is a slightly passive-aggressive colloquial expression which, depending on context, can be translated as "whatever", or "it's up to you", or "see for yourself" (i.e. "I don't agree, but I don't want to argue; it's your decision"). So when used literally it feels awkward.
So far I found this on the matter: 1. It depends on the language style: The more colloquial it is the more often the personal pronoun is left out; the more formal, the less it is left out. 2. The second factor that influences the use of the personal pronoun is the situation and the context, which means, the clearer and more obvious it is, who or what is the originator of an action, the more often the personal pronoun can be left out. In conclusion one can say that the use of the personal pronoun in the Russian language isn't a necessity and it can be left out, but in comparison with the Czech language for example this doesn't happen so often.
The English is ambivalent and can mean either that he does not know how to read or that he is prevented from reading (even though that is the less likely meaning). Without a context I don't see how you could choose one over the other.
Now that I think about it, this kind of sentence is generally written as "doesn't know how to..." instead of the simple "can't" exactly because of this. Or at least for what I can remember.
Why is "Как ты знаете, мой брат не может читать.." wrong? It marks "Как" wrong as well as "может ".
"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.