Just learning by doing without courses, etc. main-reference was selfhtml.org and looking into other peoples code.
I didn't write Node.js basics (starting server, etc.) by my own yet, because within all node-projects I'm working on someone else did this. So I only have to know how to write new services, controllers, NodeBB-plugins, etc.
But since I've looked at the basics of different projects often enough I'm pretty sure I could do this on my own now ^^
What I know about Node.js I got taught by my brother and through learning by doing and duckduckgo'ing (in my mind way better search-results than google at least for english search).
If we should help you to decide how to learn Node it'd be helpful to know what experiences you have with other programming-, script-languages