The most common and most likely answer to this crossword clue is the 9 letter word GUIDEBOOK
I've seen this crossword clue in Independent
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Buddy explains!

The straight part
We know that "leading publication?" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case leading publication? = guidebook.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 GUIDEBOOK mean?
GUIDEBOOK noun- A book that provides guidance, but especially one designed for travellers which provides local tourist information about a particular country or area.