I succedded (92%)without reading the spec for JSTL but as you could guess I read the spec for JSP 2.0 and Servlet 2.4 (not everything but a big part of it).
For JSTL I suggest you to take a look at the website of Mikalai:
http://java.boot.by/wcd-guide/. I only study JSTL on is website and maybe take a quick look on other websites.
Good luck,
ADri
PS: feel free to ask more questions