Why do you think of that? were you hired as the person that knows all of them?
Remember that as software engineers, our job is to solve problems. It doesn't matter what technology, language, or framework as long as you bring value on the table.
The question is what is it that you want to learn? based on that you will figure out what you need to learn and how you will be providing value to future employers.
Personally, I'm heading for a senior position. As a senior (in my current company, may vary from company to company) is to enable others, unblock from potential issues and mentor them on best practices and core values. Based on that, I choose where to focus my learning and what to read/research next.
Of course, I am still a software engineer and still need to learn new technologies maybe or refresh my current knowledge. I do that by reading newsletters, blogs and spending time outside my working hours to those. I will choose to go deeper into a particular technology if I think that it will bring value to our current stack. That's not required though and you can demand from your employee to provide that time for you. I'm doing it because it's my choice to do so.