similar forum devoted to learning

is there one for learning about everything

Yes.

Thanks, I just learned something!

So I’m closer to learning everything.

Well, there’s a podcast, The Complete Guide To Everything, a podcast about everything.

You’re welcome.

Need answers fast?

If you want to learn about everything an encyclopedia is much better than a forum, since a huge majority of forum posts don’t provide any learning:
https://en.wikipedia.org/wiki/Main_Page

Reddit.com has sub-forums about everything, unlike Straight Dope which discourages discussion of illegal activities.