A project box is attached to a profile only if a Wikitree Profile is managed by a Project. Normally, only the Projects add a Project box to a profile.
Are you asking about a specific Wikitree Profile or Project?
Do you possibly mean that you want to add a 'sticker' to a profile that is mentioned on some of the Projects? Those are added to profiles for many reasons, such as one to indicate a War that someone fought in, Descendant of someone, lived in a certain area, etc. There are a lot of stickers in wikitree, so more information is needed.