after taking a sec to theory craft, i think this might be the highest possible yield holy site (feel free to correct me if you come up with something better):
playing as khmer (food equal to adjacency, river adjacency)
either desert folklore or dance of the aurora pantheon
work ethic belief (production equal to adjacency)
hildegard of bingen (science equal to adjacency)
adjacent to river (+2)
adjacent to both tiles of pamukkale (+6)
adjacent to four tiles of tundra or desert depending on pantheon, (+4)
each of which contains a district, (+2)
and one of which is a government plaza (+1)
scripture policy card (x2)
(2+6+4+2+1)x2=30
30 faith, 30 food, 30 production, and 30 science, all in one district, not counting specialists
but good luck finding a tile adjacent to both tiles of pamukkale, a river, four desert/tundra tiles AND knowing of it before even picking your pantheon...!!