Definition
Used to introduce something that the speaker particularly wants to know or find out.
最想知道的事情
If there's one thing I want to know, it's why they are moving.
如果有一件事我想知道，那就是他们为什么要搬家。
If there's one thing I want to find out, it's what the actual budget for this project is.
如果有一件事我想弄清楚，那就是这个项目的实际预算是多少。
If there's one thing I want to know, it's whether he was telling the truth.
如果有一件事我想知道，那就是他是否说了实话。