First of all, here I want to share with my point of view on job position, it can be called different ways "Senior Frontend Developer, "Strong Senior Frontend Developer", "Frontend ninja", "Frontend Jedi" and etc but this one means - a person with huge experience and knowledge in frontend development.
I'm going to share the topics list which I think this person should know, I'll also mark how deep this person needs to know this topic. It looks like "deep: 100%" and it is just my point of view on section knowledge. Sure, it does not mean that it is a constant, there are many things which will impact on it, for example: your company can produce web sites or online games and potentially you will have a different level of many sections but on average I see it this way.
This is foundation of everything in frontend world. So, I guess, everyone understand how important they are, without it you cannot understand many of frontend technologies.
Every developer has a favourite framework and every developer has to know it well, not only framework but ecosystem as well, the most popular libs, cli, the best patterns and approaches, and even time to time look into source code of it (I heard opinion from guys "if you didn't read the source code of framework you don't really know it" but, as for me, I don't follow that rule).
The frontend world is too big and to know only one framework means to build walls around yourself. If you know one more framework on a good level, this is a big plus to you. When I say "good level" I mean you can take a part in project with this framework without problem. Yes, maybe you don't know some aspects about it, that's ok.
New framework is a new vision of resolution for the issues. It's useful to know two frameworks on good level and several on idea level (when you know ideas which stay behind the frameworks, for example virtual DOM, two way data binding).
This is another base of everything. If you know how to write a code but don't know how to design it for the best using, your knowledge is not very valuable. I understand there are many patterns and design approaches but we really need to know main of them.
Ok, guys, some frontend developers think they don't need to know anything about security because all security should be on backend side.
But no, we can do a lot of security on frontend side. And if you know top 10 of OWASP you are good and if you know how to protect from them you are the best.
Computer science is a language for all developers and it is a basic of our profession. It can be seems that frontend work is not about difficult algorithms and data structures but it's totally depends where do you work and what do you code. Frontend side becomes more and more complicated, we work with games in browser, graphics, complicated data from backend also we shouldn't forget that top of IT companies demand knowledge of algorithms and data structures on interview.
Hey, it is very simple, animation is our daily work part. People admire the awesome animation in their devices. Even harsh enterprise projects start to include more and more animations to their interfaces.
Every time when you do accessibility in your website you get one point to your karma. All jokes aside the accessibility very important thing, because it's about people. Imagine the situation, you go to the shop to buy some food but you can't because you are too big and door is too small and you can't go inside, it's insulting, isn't it? Keep this feeling in your mind every time when you don't want to spend time for
Besides a lot of countries have a law about web sites accessibility.
First of all you, as developer, need to speak with UI/UX specialist and you both have to understand each other, secondly you, as developer, work with design and you can see some details and advise how to make it better.
So, TypeScript becomes popular and the case that you will get next project with typescript inside highly likely. Or you will be a person who inject it to the next project.
All this is exclusively my point of view according my experience and acquired knowledge. I work in a service (outsourcing and outstaffing) company and, of course, my experience connected this direction, your point of view may differ if you work in product company or some where else.