Here are Luigi’s Mansion 3 gem locations for every floor (B1, B2, 1F, 2F, 3F, 4F, 5F, 6F, 7F, 8F, 9F, 10F, 11F, 12F, 13F, 14F, 15F). Each section has a locations list followed by specifics for how to get gem so you can have hints and full answers.
Source: IGN.com Luigi's Mansion 3 Gem Locations for Every Floor