▲分析：

主句：You can’t expect to learn all

从句：there is to know about the subject in a 45-minute lesson（定语从句）

定语从句中的不定式短语 to know about the subject 为定语，修饰定语从句被省略了的先行词 that。比较：

There is a lot to know about the subject.

→all there is to know about the subject.

→You can’t expect to learn all there is to know about the subject.

▲句意：

You can’t expect to learn all (that) there is to know about the subject in a 45-minute lesson.  你不能指望在45 分钟的一节课上学到这门课程的所有内容。

▲为便于理解，再给出以下相似例句：

She knows pretty well everything there is to know on the subject. 对这个问题她几乎了若指掌。

One can never learn all there is to know about cooking, and that is one of the joys of being a chef. 钻研烹饪之道是永无止境的，这也是当厨师的乐趣之一。