To my surprise, when browsing through the package contents for the app on MacOS, I discovered that the Official Strategy Guide (i.e. hint book) for Curse of Monkey Island is in fact included in the GOG package in addition to the manual, even though the strategy guide is not listed anywhere on the store page and does not appear as a downloadable file in the "Extras" list for the game either on the website or in GOG Galaxy.

In my GOG Galaxy installation on MacOS, the full path to the guide is:

/Applications/The Curse of Monkey Island™.app/Contents/Resources/game/game/Guide.pdf

It is 75mb and 226 pages — a very thorough hint book with lots of fun additional content too.

Enjoy!

It's also on the Windows release, sitting there on the installation folder. Quite nice indeed. GOG should advertise this goodie, it's worth the fuss