What does 课文放大镜 mean?
課文, lit. 'the text of the class' or 'class text', simply refers to the text you just studied for class.

放大鏡, lit. 'the mirror that magnifies', means magnifying glass.

課文放大鏡 is a compound noun with the first noun behaving like an adjective. That is to say, you can think of this as equivalent to (and more compact than) 課文的放大鏡, meaning 'the magnifying glass of the class text'. (In fact, if you think closely, even 課文 and 放大鏡 themselves are compound nouns.)

You examine something closely with a magnifying glass. 課文放大鏡 therefore is a figurative way of saying 'a close look on the class text'. The questions guide you through the text you just studied, and are thus analytical. More formally, you may say 課文分析 or 文本分析 which means 'textual analysis'.

However, you probably won't find this in dissertations or higher-grade class texts. That is because 課文放大鏡 is a light-hearted, informal saying.