Magento 2, certification exam
Update 2018-04-30:
Magento U has now released three Magento 2 certifications. There's also a Frontend Developer Certification under work that should be available within several months, and I've heard rumor of a JS Certification a year or two down the road. You can view all certifications on the Magento U website.
Study guides for each certification can be requested here: Download A Free Magento Study Guide
The available M2 certifications are:
Magento 2 Certified Solution Specialist: "Magento 2 Certified Solution Specialists have demonstrated a thorough understanding of how to leverage Magento 2 functionality to satisfy ecommerce business goals according to best practices."
Magento 2 Certified Professional Developer: "Magento 2 Certified Professional Developers have demonstrated a deep understanding of how to customize Magento 2 source code in accordance with Magento best practices." This is targeted at backend developers with 1.5+ years experience with Magento 2.
Magento 2 Certified Associate Developer: "This exam is for a developer who is beginning their career as a Magento Developer and is designed to validate the student's skills and knowledge of Magento 2 in the areas of: UI modifications, database changes, admin modifications, customizations, catalog and checkout structure, and functionality changes."
Upcoming: Magento 2 Certified Frontend Developer
Original Answer:
There is no Magento 2 certification exam yet, so there are no resources for studying/training for the M2 certification exam. Anything saying otherwise, as of this writing, is lying.
The latest rumors I've heard are that M2 certification will be coming sometime after the release of Magento 2.2. It's likely M2 certification will be released in late 2017 or early 2018.
See also: Certification and training - Magento 1 vs Magento 2
You can get sample study guide from below link, Which is written by Joseph Maxwell and he is one of the first to have taken and passed the Certified Developer exam
It has 177 pages full of helpful and informative content. This not only makes you a better developer, but will help you pass the test.
https://swiftotter.com/technical/certifications/magento-2-certified-developer-study-guide