1. There is a number of SEOs who have a good grasp on technical SEO for static HTML, but what will make you different in this competitive world is:
• Knowing how JS works
• Where it helps SEO?
• Where it blocks or restricts SEO?
• What kind of effects are on search engines & clients?
Having these skills will make your services much more valuable.
3. Meanwhile websites built with React, Angular and similar JS based technologies may be something you have to work on at times. Without the knowledge of JS you'll find it much harder to figure out how to get these sites properly indexed and optimized.
4. You may also encounter some smaller issues related to how a page functions related to JS, where certain content is not getting indexed. You may even want to leverage JS to do this on purpose in some rare cases.
6. You don't need to be an expert front end developer, but some knowledge will go a long way to making you stand out compared to more average SEO professionals.
While writing this article I came across a case where there was a comment on a blog but it was not shown on the front end i.e. on the blog but when I saw its source code the comment was written there and that was because of AJAX. So as a normal SEO Expert someone could lost an opportunity to get a back-link from there but an smart SEO Professional having a little bit knowledge of JS and AJAX can have this opportunity in hand to get a back-link from there also.
The answer is “No”.
The answer is “YES”.
The answer is “It depends”.