Hi Fahmi101
welcome to this Apple (user-to-user) Community!
Re: "My iTunes Digital Booklet missing from purchased albums"
In what file format are the digital booklets published ? (Eg: .pdf .epub)
The way I understand it ... booklets are in a different file-format than music files ... you may need to look in Apple Books to view any digital booklets.
If they haven't downloaded there automatically, you may have to manually re-download them to an app (like Apple Books or maybe on iPhone you can use the "Files" app ) that can "read" the files and allow you to view them.
Are the booklets listed in your purchase history ?
This discussion on a similar topic has a useful reply from a Community specialist: Digital booklet - Apple Community
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If needed:
How to: Redownload books and audiobooks - Apple Support
How to: Redownload music from the iTunes Store on your iPhone or iPad - Apple Support
What to do: If there’s an issue when you redownload apps, movies, or other content from Apple - Apple Support
All the best!