can you climb to the top

Yes once its open again

Its closed but it will be open again soon

Yes you can

I would take the elevator, unless you're Alain Robert.

Its closed for now but will open and you will be able to climb

Yes. you can go to where the window is. But check to make sure they are open.

It is closed for renovations now, but when it re-opens, yes, you can climb to the observation deck.