Hey,
The questions asked in the NEET include the syllabus of class 11th and 12th Physics,Chemistry and Biology. Organic Chemistry is one of the most scoring sections of NEET and "reaction mechanism" is the essence of it. You need to understand the basic principles of organic Chemistry if you want to ace reaction mechanism. You can go through the previous years question papers in order to get the idea of the questions asked in the exam. Make sure, you are thorough with the concepts of Chemical Bonding,general organic Chemistry ,isomerism as they will help you in reaction mechanism. You need to practice a lot if you want to score good in this section. Organic Chemistry by OP Tondon is one of the best books for the preparation.
For detailed information follow the link given below:
https://medicine.careers360.com/articles/neet-syllabus
Hope this helps.
Good luck.