Be sure to review the topic areas in the outline that is listed on the JNCIS-SEC section of the certification site.
https://www.juniper.net/us/en/training/certification/certification-tracks/junos-security-track?tab=jncisec
Pay close attention to the section called "Additional Resources"
These docs all contain a specific factoid, situation, issue or nuance configuration that shows up in test pool questions.
Sign up for a Junos Genius account.
https://cloud.contentraven.com/junosgenius/login
Use the outline above to location the topics in the video material loaded here.
Consider a Junos Genius plus subscription to get the sample test for JNCIS-SEC.
I've found these are an accurate reflection on ability to pass the real exam.
But don't just continually take the test, the pool is too small and you end up just memorizing those questions and not learning the concepts.
Best of luck.