Im a ST student, what is the minimum percentage i need to get to be able to apply for jee examination?

There is no percentage barrier to be eligible for Jee Main. The basic eligibility critdtia is that the candidate must have passed 10+2 with Physics, Mathematics as compulsory subjects [along with one of Chemistry/Biotechnology/Biology/Technical/Vocational] from a recognized board. For admission to IITs, NITs, IIITs, CFTIs, a general and OBC candidate need to have at least 75% marks in the qualifying examination or be in top 20 percentile of the respective board. And it is 65% for students belonging to SC, ST or Pwd categories. For B.Arch, candidates should have passed 10+2 or equivalent exam with minimum 50% aggregate marks from a recognized board. For B.arch, candidates should have passed in Physics, Chemistry and Mathematics and Only compulsory subject for B.Plan is Mathematics. But for this year, the 75% criteria or being in top 20 percentile of respective board has been withdrawn, so if you have cleared Jee Main qualifying cutoff, then you can appear for Jee advanced. For admission to NITs and other centrally funded Institutes this criteria has been withdrawn, only for this year i.e. 2020-21 session.
http://engineering.careers360.com/articles/jee-main-eligibility-criteria/amp