I suppose one idea would be to mark out in the book, the example as important (with a star or bracket symbol or highlighter), and then, as photoread4me says, put the page number on your mindmap.
I can see the problem you're having, as I'm starting to experience something similar as I'm trying to learn C++ and Python.
For MindMapping, I mostly use an application called Freemind. (Its opensource, and runs on Windows, Linux, and Mac).