This question already has an answer here:
What is the process for requesting a feature (that already exists on some SE sites) for a site that doesn't yet have it? I'd expect the default forum would be a question on the site's own meta, but I don't know if the moderators there would necessarily have the power to effect a requested change if they wanted to.
As a concrete example, this question on meta.puzzling is asking for code syntax highlighting (as already exists on SO) for the puzzling site - would such a request need to be raised on meta.SE to be seen by someone capable of considering and delivering that change?
Apologies if this is covered by existing documentation somewhere - I couldn't find it anywhere but I'd be very happy to be pointed in the right direction :).