My friend has been playing the Japanese video game called Persona 5 and there was the high school named 秀尽学園高校. I can't find the word 秀尽 (shujin) anywhere. Does it mean something?
It's just another proper noun meaning nothing in particular. It's a combination of random common kanji with nice meanings. 秀尽 is a combination that probably had not existed before, and sounds realistic and natural enough as a Japanese proper noun. That's what's needed for a fictional school name, isn't it?
秀尽 is homophonic with 囚人 ("prisoner"), but I don't know if this was intended by the author. I know prison is an important motif in Persona 5, but homophones are very common in Japanese. If I remember correctly, although some students were "jailed" at the beginning of the game, I feel it's excessive to link the entire school to a prison.
See Also: Parsing a fictional place-name