Languages compiling/interpreting to Javascript (such as Ruby/Python/Coffescript)
You shouldn't even need to understand the syntax of Javascript. Just an understanding of the DOM should suffice. Having said that, all the DOM examples will be in JS syntax, so reading them will be tricky. Being able to debug the transpiled javascript is also usefulo
Correct. You can write a server an client with javascript in all the places
Also correct. This is probably a better option, as these languages map more closely to the underlying javascript.
Newbie self-learner diving into web development here.  My goal is to learn how to build web-apps.  Three quick questions:  

Ruby and Python seem to have offshoots that compile their respective code to Javascript (i.e. Opal/Pyjamas).  If I can get an understanding of the DOM, i.e. the DOM, do I have to even learn the full language of Javascript or can I just rely on Ruby/Python compiling to JS?
Everyone seems to be talking about node.js allowing for javascript on both the browser and server.  Does that mean that if I know Javascript and use Node, I don't need python or ruby for web dev?
If node.js allows for server/client side javascript, couldn't someone just learn something like Coffeescript or Typescript and throw python, ruby or php aside?