He admits he doesn't even know when his brother is in town.

他承认甚至不知道他的兄弟什么时候在镇上。

《柯林斯英汉双解大词典》

It's a bit inconsiderate of her not to let you know when she expects to arrive.

她不让你知道她什么时候会到，这样做有些不体谅人。

《柯林斯英汉双解大词典》

I know when you fall asleep.

我知道你的入睡时刻。

youdao

Many people who come to Las Vegas in hopes of winning lots of money do not know when to stop gambling.

VOA: special.2010.03.14

But I know when I multiply a vector by a number, I get a vector in the same direction.

但是我所知道的是当矢量乘以一个常数,我会得到一个同方向的矢量

耶鲁公开课 - 基础物理课程节选

So I know when I was in New York working as an intern I would go there every week

所以我在纽约当实习生的时候就知道，我每个礼拜都会去那里。

关于购买艺术品 - SpeakingMax英语口语达人

It is impossible to know when a society has reached a breaking point until it happens.

BBC: The Greek conundrum

Do you know when you should drop one of your two health insurance plans?

FORBES: Sidelines

But how do you know when someone is telling the truth or is lying?

FORBES: Are You Being Lied to on National Honesty Day?