You had better make a mark when you have any questions.

每当有什么疑问你就做个记号。

While reading, I often make a mark where I have any questions.

读书时，我经常会在有问题的地方做记号。

Please make a mark where you have a question.

请在有问题的地方作个标记。

Make a mark where you have problems.

在你有问题的地方做个标记。

Make a mark where you have questions.

在有问题的地方做个记号。