How is の being used here?
今日は、色々な日本一と世界一の話をしました
Source: https://cijapanese.com/no-1-in-japan-vs-no-1-in-the-world/
How is の being used here?
今日は、色々な日本一と世界一の話をしました
Source: https://cijapanese.com/no-1-in-japan-vs-no-1-in-the-world/
This の marks the genitive case. You can read more here.
Here, と is used to list nouns exhaustively. Nouns that are listed by this と create a noun phrase and can therefore occur in places where nouns can:
Note that 話をします is a verb phrase consisting of a noun, 話. This noun is modified by this other one 日本一と世界一 through の, meaning "a talk about Japan's best and the world's best."