I finally passed my Jenkins exam yesterday. It took a week to prepare for the exam. As always I created a github repo available by the link:

https://github.com/smartrus/certified-jenkins-engineer-study-guide/blob/master/certified-jenkins-engineer.md

The main course that I relied on was LinuxAcademy's Certified Jenkins Engineer course. It has awesome practical lessons and labs to complete. However, the final practice exam is too oversimplified, I got very tough questions regarding Pipelines and plugins.

The following other resources that I used to prepare are:

Certified Jenkins Engineer - Quizlet flashcards

Good luck!