When exactly did the incident occur?

这一事件究竟是什么时候发生的？

《牛津词典》

When exactly is it?

这具体在什么时候？

youdao

Students should not worry about when exactly to use certain expressions.

学生不必担心什么时候使用某些特定的表达。

youdao

When you hit the nail on the head,exactly on its top, it goes into the wood perfectly.

VOA: special.2009.09.20

Now, when exactly did the American South become a slave society?

那么美国南部究竟是从何时起成为奴隶社会的

耶鲁公开课 - 美国内战与重建课程节选

We'll talk about exactly what a gel is later when we talk about biomechanics and cells are suspended within it.

之后当我们谈到生物力学的时候,会具体讲讲这个凝胶是什么,以及细胞是怎样悬浮在其中的

耶鲁公开课 - 生物医学工程探索课程节选

Where is this so-called hard landing, Mr. Chanos, and when exactly is it supposed to occur?

FORBES: Barclays: China Source Of High Inflation For "Next Decade"

But the agreement is ambiguous about when exactly any reforms may come into force.

ECONOMIST: Another splendid compromise forged in Brussels | The

Experts argue about when exactly the system will begin to pay out more than it takes in.

FORBES: Fact and Comment