Is there a Chinese equivalent of the German "Mut zur Lücke"? In German, we have the expression "Mut zur Lücke", in English something like "courage to have a gap" - a knowledge gap. It is used between students, when they skip to learn something for an exam.

It's more the hope that this topic will be not part of the exam or test. So it is some kind of taking a calculated risk. The reasons can be diverse. Normally caused by the inability to understand or simply running out of time. Laziness or carelessness  also play a role.

When someone says this, they stop learning (of a certain topic) and accept the risk that it maybe be asked in a test. Then of course they "knows their limits", but this is secondary. They are brave / have nerve to have a knowledge gap.

Is there a similar expression in Chinese? I even could not found a translation for "knowledge gap" in Chinese.
google told me "Mut zur Lücke" means "dare to venture into the unknown", and I can't find a Chinese phrase that have the same meaning xD. But there is a expression, 碰运气, which means to "push your luck". So in your example about the exam, you can say 碰一碰运气吧，这部分我不复习了(Let me push my luck and skip this part).

P.S. In Chinese, 人品 means moral qualities. Chinese people sort of believe in karma, where people with good qualities(人品好) will do good deeds, good deeds will be rewarded with good luck. So you can replace 碰运气 with 拼人品(the collocation can't be changed, 碰人品 and 拼运气 are not proper expressions). But this expression "拼人品" is informal and is only used among young people.