"Since there is too much for any web developer to know, what is the most graceful and professionally acceptable way of not knowing things?"
I think the answer is honesty.
It's okay to say that you don't know stuff. My workplace pits me against the Great Unknown all the time: a huge complex monster of a core product. Internal tooling inherited from another team. Custom hacked docs generation, all undocumented. Legacy Code. Almost all of it is written in TypeScript, which I don't even consider my strongest language.
While I can always look up syntax I don't know online, I can't do the same for our own concepts. That's when I ask for help. I admit that I don't know all the things. And that's okay.
It's okay to ask questions. It's normal to not know all the things. If I can be honest about the things I don’t know, so can others. And if everyone does, it creates a office culture of helping each other out - gracefully and professionally.