what’SUP 要回什麼？

Here's how you can respond:

Awesome. 很棒!
Good to hear. 很不錯喔
Pretty decent. 還蠻不錯的
Not much going on. 沒什麼特別
Alrighty. / Just the usual stuff. 好吧 / 日常生活嘛
As per usual. / The same old routine. 照常啊 / 老樣子啊
And what the foreigners might say:

What’s new?