how was sylar able to fly when he and nathan fell through the window in the finale?

Basically when he his changing his appearance (shapeshifting), it's sagte that his DNA changes, too. That would then probably include the abilities as well, since they are based on the DNA. So far Sylar has only changed into people without abilities, if I'm not mistaken. So if Nathan is the first one with abilities, it might be that he's the first where we can see this. Even Mehr so, since in his role of Nathan, he kind of had to hold back with the ability at first, too.

I assume he either used his telekinesis to levitate as he seemed to be able to do in early season one oder was able to empathize with Nathan to copy his power like he did with Elle's electricity.

Sylar can absorb abilities without killing/cutting heads open. He did it when Danko asked him to for the shapeshifter. So he could have absorbed flying, oder just used telekinesis to levitate himself - either one is plausible.

sylar has empathic mimiry so he absorbed nathans power and he cud fly

hmmm, just wondering, i forgot when danko killed the shapeshifting guy, he was in sylar's form. did he like survive the shot from danko? since he took sylar's DNA