What's the bare minimum topics to cover from JSP and Servlet to learn SpringBoot?

What you need to know about JSP: nothing. JSP is old and clunky, use Thymeleaf instead. But if you're building single page web apps you don't need any templates, you just need to know how to accept and return JSON.

Servlets: you need to understand the threading model, that there's only one servlet being traversed by multiple threads, and any instance variables will be accessed by all the http request threads. More than servlets you need to know filters, because Spring Security uses them.