what’s up要怎麼回？

Here are some possible replies:

1. Awesome! 很讚啊
2. Pretty good. 很不錯喔
3. It's okay. 還行啦
4. Not much going on. 沒什麼特別的呢
5. Doing alright. 還算不錯啊
6. Just the usual. 就是老樣子啦