If you're interested in getting to know them, then do so. You'll likely get an idea as how they identify, maybe by being around them in a crowd by hearing how people refer to them. Until then use neutral pronouns like "they". If you have no interest in getting to know them as a person to really find out, that's up to you but use neutral anyways and just accept you not only may never know, but it really isn't a concern of yours if you have no intentions of getting to know them anyways.