This might be grossly simplifying things: but if you're already familiar with "old JS" (since you mentioned jQuery), to read and write ES6 code in most modern JS projects, you really only need to get used to a handful of concepts: 1) lambda functions and the fat arrow syntax and what it does for scope, which is used extensively in modern JS codebases; 2) Promises/promise chains and async/awaits; 3) certain widely used new keywords like const and let, how requires and exports work in node.
This doesn't include frameworks like React which is its own entire separate category of things. But at least you'll be comfortable with ES6 and node8+ at this point. If you're more interested in frontend modern JS unfortunately you'll also probably have to learn about babel and webpack and the like.
