(So) what's with the hat? [=why are you wearing that hat?]（那）为什么戴那顶帽子？

He told me to go away. What's up with that? [=why did he do that?]他叫我走开。这是为什么？

What's with him?他怎么了？

What's up with you? You look upset.怎么回事？你一脸不高兴。

I can't figure out what's up with this computer.我搞不清楚这台电脑出什么问题了。