CNB is usually given for crew change. Technically, it's possible for a train to skip CNB since the current station of Kanpur lies on a slight loop from the main NDLS HWH line. A stoppage can be given at Holding Line instead[IIRC, One train even does this]. PRYJ and BSB are skippable since DDU serves both for crew change and serves the city[though in practise, I am not sure if any train skips BSB].