The most current version is ES10, so you should learn ES10. Next year it'll be ES11. The current version of js includes all the features of the previous versions. You'll only miss out on things if you learn an outdated version.

I should add that learning a version of js isn't really the correct way to go about learning js. For example: an ES10-specific feature is "Object.fromEntries". It's the reverse of an ES8 feature called "Object.entries". Object.entries is a simplified for-in loop, which is an ES1 feature. You can't really say you truly understand Object.fromEntries unless you also know how to use Object.entries, and a for-in loop. That requires learning an ES10, ES8 and ES1 feature.

So, it's not as clear-cut as picking a version. You'd have to learn all of it. I'd recommend http://javascript.info.