RRB NTPC cut-off marks are published on your regional RRB website along with the result.
Separate cut-offs are announced for UR, OBC, SC, ST and EWS categories.
The cut-off PDF lists the minimum normalised marks needed to qualify for the next stage.
Download the official PDF from the RRB website, not from WhatsApp forwards.
Cut-offs change every year based on vacancies and paper difficulty.