The most common and most likely answer to this crossword clue is the 6 letter word CAHIER
I've seen this crossword clue in The Times
C
A
H
I
E
R
More clues leading to the result CAHIER
Buddy explains!

The straight part
We know that "notebook" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case notebook = cahier.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does CAHIER mean?
CAHIER noun- A number of sheets of paper put loosely together; especially one of the successive portions of a work printed in numbers.
- A memorial of a body; a report of legislative proceedings, etc.