When i am missing the same type of questions all the time, i write the questions and how to solve the questions so that i never make such a mistakes in the future. And the note book is my useful study material. How can i call the note book?
'Notebook' is all I can think of. When someone else compiles a list of answers to common questions/problems it's called a 'crib-sheet', but when you compile your own crib-sheet, that's a way of cheating in exams!
About 100 years ago people used the Latin phrase 'vade mecum' (= 'go with me'), but nobody uses that now.
On the web, you may have come across the term 'FAQ' - Frequently Asked Questions (with, of course, answers).
But for your purposes I can't think of any improvement on 'notebook'.