For State Eligibility proof in JOSAA counselling the documents you need are the  12th Marksheet /Pass Certificate for IITs or Aadhar for NIT+ system or copy of Passport in case of PIO candidates.

To know more about the JOSAA Counselling visit the link below:

https://engineering.careers360.com/articles/josaa-counselling

I hope this answer helps. All the very best for your future endeavors!