You have posted:
-"Who is an "Audit Officer " here. ??
We are not aware. It is believed that this may be a superior/final authority. You may enquire and confirm from your office.
-"Is obtaining information via RTI from DoPT is preferable??"
Ideally the amendment /updation /insertion/modification/introduction/changes should be circulated to employees. Your establishment may have the practice of posting on website, or issuing circulars to section officer and your section officer may be having latest rules in force. You may enquire and confirm from your office, from whom the latest rules can be obtained, and obtain a copy. Otherwise you can apply in writing and obtain a copy from admin/HR/personnel cell.
RTI route is preferable in the sense that you shall get authentic and certified copy from the competent resource.
Your have mentioned that "When i enquired with our Section Officer, they said I am not eligible as it is for only Group A and B officials." Whereas from the soft copy downloaded and attached by you it does not seem so. Therefore your section officer is either wrong or right.
-"What would be the next step if i can not be given Study Leave even if i am eligible????"
As per procedure in your establishment you may escalate to the next authority.
It is felt in a central govt establishment like yours the leave sanctioning authority shall grant leave by adhering to set rules in force or decline by citing set rules in force.
It shall be appropriate to obtain latest rules (which is your right also) and proceed as per rules. Your chances of success shall be better.
Valuable advice of learned experts/members having mastery on central Govt, CCS, DoPT. rules is sought.