Why not "I can read"?
wouldn't 'I can read' be 'posso leggere'?
"I can read" is correct and Duolingo has already accepted it.
Why not "I know to read."?
It actually is good English, but it means something else. When you say "I know to read," it actually means "I know that I am supposed to read."
Agreed. A different context than the lesson, but correct. As in, the instructor asks "What do you know to do first, before you ask a question about this lesson?"
"I know to read."
That's the literal translation but it's not good English.
What about "So come leggere?"
You don't need the «come» in Italian and in many other, if not all, Romance languages. When you say «So leggere.», «So l'abilità di leggere.» is implied.
It is sensless that they mark a correct translation wrong for an answer that has a diffedrent meaning.