Sorry, I can't agree with the above (pun intended!)
According to dictionaries one of the definitions of can is precisely,
"to know how to:
He can play chess, although he's not particularly good at it."
Apart from the general "you", if I said to someone, "Can you ..............?" I would almost always be asking about ability, not if they have permission to do something. If you say "Can you speak Japanese?" you are asking if they have the ability to speak Japanese, not if they have permission to, unless you were being very specific, eg. "Can you speak Japanese in class?" but I would quite probably have to clarify and make sure someone knew I was meaning "Are you allowed to speak Japanese in class?"