The book does cover 1.9. Ruby 1.9 was new back then, so the text could use some refreshing by now - but most stuff in the book is definitely still relevant.
There are a few things I would change, but they barely have to do with the internals of Ruby. I’d like to take away some metaprogramming tricks that turned out not to be so widespread in practice, and I changed my mind on the way that some other tricks should be used. Still, I don’t think that it’s time for an update just yet.
I don’t know rails yet, is it ok to skip the rails part until I start learning rails?
Oh, I just used the Rails source code to come up with examples. I didn’t have to be a Rails expert to write it, so I guess you don’t have to know Rails to read it. ;)