Nothing "happened to" the Semantic Web. It's here, and it's growing in utility and capability as the technology matures. What isn't necessarily growing is understanding of what the Semantic Web really is, who it's for, how to use SemWeb capabilities, etc.
I'll accept some responsibility for that last bit, as somebody who has been active in promoting, and advocating for the adoption of, SemWeb tech. I could do more / do a better job in that regard.
I think the general understanding of the need for formalized semantics on the web is going to grow when people realize that chatbots think the answer to "name a fruit that isn't orange" is "an orange": https://hashtag.ai/blog/2018/09/23/fruit.html
Well, now's as good a time as any to start! Let's say I wanted to throw a layer of semantic markup over an existing site - where would I go to figure out what schemas to use and how to use any given schema (it's been a while since I tried to SemWeb up a site.)
That's an interesting question, because it has a few assumptions baked into it. I'd love to write a long eassy on that right now, but I don't really have time. But to answer the core question, one good place to start familiarizing oneself with the various schemas that are available is:
I'll accept some responsibility for that last bit, as somebody who has been active in promoting, and advocating for the adoption of, SemWeb tech. I could do more / do a better job in that regard.