I completely forgot about Norway, sorry. Thank you Tannhauser. Yes, +32 with Norway seems to be the maximum with the natural wonder.
So if I remake the list of maximum adjacency (hoping that I'm good now, correct me if I'm wrong!):
Campus: +28 Science and +28 Production (Netherlands only) (nearly impossible: involve a lot of luck)
You need a river (+2 Science, Grote Rivieren ability), six adjacents Geothermal Fissure (+12 Science) or four adjacent Geothermal Fissure (+8 Science) with the natural wonder "Pamukkale" (+4 Science), making it +14 Science, +28 with Rationalism policy (+100%). The dedication "Heartbeat of Steam" allows to have Production from Campus adjacencies.
Without Geothermal Fissure, it is +20 Science, possible by Brazil (Pamukkale and 4 rainforests), or Netherlands (Pamukkale, river, 3-4 moutains, 0-1 Government Plaza).
Commercial Hub: +51 Gold (and +51 Science) (Mali only, Suguba)
You need a river (+2 Gold), six adjacent Holy Site (+15 Gold), making it +17 Gold, +51 with "Harbormaster" Reyna's title (+100%) and the Towns Charters policy card (+100%). The dedication "Free Inquiry" allow to have Science from Commercial Hub adjacencies.
Harbor: +30 Gold (and +30 Science and +30 Production) (England only, Royal Navy Dockyard)
You need a City-Center (+2 Gold), a Governement Plaza (+1 Gold), so 2 districts (+1 Gold), four adjacent marine ressource (+4 Gold) and be on a foreign continent (+2 Gold), making it +10 Gold, +30 with "Harbormaster" Reyna's title (+100%) and Free Market policy card (+100%). The dedication "Free Inquiry" allows to have Science from Harbor adjacencies, and the Shipyard building allows to have Production from Harbor adjacencies too.
Holy Site: +32 Faith (and +32 Science) (Norway only)
You need the natural wonder "Hubsunur Hollow" (+4 Faith), four adjacent woods (+2 Faith), the pantheon "Danse of the Aurora" (+6 Faith, Hubsunur Hollow counts as toundra), and four adjacent woods with Stave Church (+4 Faith), making it 16 Faith, 32 with the Revelation policy card (+100%). The great Scientist "Hildegard of Bingen" allows to have science from a specific Holy Site adjacency.
Industrial Zone: +63 Production (or +126 Production) (Germany only, Hansa) (nearly impossible: involve a lot of luck)
You need six adjacent Commercial Hub (+15 Production), and having under each Commercial Hub a Strategic Ressource (+6 Production), making it +21 Production, +63 with the Craftsmen policy card (+100%), and the Collectivism dark age policy card (+100%). The Coal Power Plant building allows to have Production from Industrial Zone adjacencies.
Without luck, it is +45 Production, +90 with the Coal Power Plant.
Theatre Square: +52 Culture (Netherlands only)
You need a river (+2 Culture, Grote Rivieren ability), six adjacents wonders (+12 Culture), one of the wonder must be the Machu Picchu (+1 Culture from mountain), making it +15 Culture, +52 with the Grand Opera policy card (+100%) and Vilnius suzerain's bonus with a level 3 alliance (+150%) (technically: +52.5).