I don't know.
我不知道。

I'm not sure.
我不确定。  (收集:http://www.com10.cn)

Who knows?
谁知道啊？  (整理收集:英语作文网)

Don't ask me!
别问我！  (http://www.com10.cn整理收集)

It's not certain.
还不确定。  

Nothing is set yet.
事情都还没有定案。  (整理收集:英语作文网)

It hasn't been decided yet.
还没有决定呢。  (整理:http://www.com10.cn)

It's not clear.
事情还未明朗。  (英语作文网收集整理)

It's up in the air.
情况还混沌未明。  (收集整理:英语作文网)

It's hard to say.
很难说。  

(整理收集:英语作文网)

(整理收集:英语作文网)