I've read this manga a long time ago and I don't even know where I stopped so I hafta read...

i think the only one who knows he's zero is that pink haired chick from earlier (the one that's in love with him).

Awww I wanted them to realize sooner or later. But thanks! (=・ω・=)

they might still find out later, but as of now it's just pinky

Somebody did yes

the chairman also found it out .. that's why zero is the new teacher of S class ...

i mean other than her

if i based on what i read on the manhwa , aside from the pinky girl and the chairman, i believe no knows yet. well if were basing on humans. but on the monster side i think the blue dragon who was so afraid to zero knows too.