Hello!

Many free mock tests are available for AIIMS exam on various sites on the internet. There are various guides available in the market as well. If you go to any coaching institute, they can provide you with sample papers. The official website of AIIMS also provides a few sample questions which can help you gauge the difficulty level of AIIMS exam. 

Check out this link to know more about the AIIMS exam-

https://medicine.careers360.com/exams/aiims-mbbs

All the best!