As a beginner programmer (a.k.a. CS student) I was able to pickup the basic of the language in the last 2 months and work on a real world (not a school project, it's a library that other universities use) cuda c++ project. I read a book so I have an idea of what can and can't be done, but when I need to implement something unusual (ie function object) I need to lookup it in the book or ask for help to my mentor. I still need help to understand gcc errors, cuda uses an "old" version (3.4 I think) so we don't get the improvements of the new versions.

Yes, you always need to look things up.

In the projects I take part on, with teams from 20 - 100 developers, you cannot know everything regardless of the language.