Sylar first uses the freezing power in the online comic - to freeze a road, wiping out a few cop cars. I can't remember if he also got the power in that same comic (from the truck driver who's truck he stole).

He definitely does not have the ability to tell or "see" that someone has a power - someone has to tell or show him. That's why he wanted Suresh's list so badly. Also how he killed Claire's friend thinking it was her. He's probably a great cheerleader now though.

The writers *should* have done something similar to Sylar's super-hearing headache with Peter, but they didn't. They're not perfect and sometimes small details slip through. But I'm fairly certain that doesn't mean he doesn't have the power (and the others Sylar has).

The ability to break down and liquify matter, like the telekenesis, isn't something passive, so I suspect he'd have to try to use it before it could be used. Not knowing the power is there is obviously a bit of a hinderance...

BTW, I'm writing in this pseudo-reality way because it's simply easier to do so (not having to write the word "character all the time, etc), not because I'm so wrapped up in the show I have a hard time distinguishing TV from real life.