Yes, RTI can be filed to know the Cut off marks in the exams...
In the decision of the Central Information Commission in the case titled Subhash Chandra Tyagi vs
CBSE bearing no. CIC/SA/A/2016/001451, it has been held that every person has a right to know the genuineness of his degree and education and hence all qualifying examinations, degrees and marksheets are public information under the RTI Act.