what should be the percentage in JEE mains to secure a du , dtu or nit

NITs such as Warangal, Surathkal, Nagpur, Rourkela, Trichy are top rated. For getting into the top NITs you need to secure at least a rank within 7000 to 8000 and the respective percentiel lies around 99.5 to 99.6. For getting Computer Science in those NITs, you need to score at least 99.7 to 99.8 percentile as the cutoffs for Computer Science is usually high. For CSE in NITs such as Jalandhar, Raipur, Patna, Silchar, Uttarakhand etc you must score around 99. 3 percentile. You haven't mentioned your state quota. The cutoffs for state quota candidates are usually low.
DTU, being one of the best Engineering colleges the cutoffs are enough higher. For top branches in DTU, you must secure a rank within 2500 or 99.8 percentile in Jee Mains through all India quota. And within 4500 rank for home state candidates. Last year, 11137 was the highest cutoff closing rank for DTU for general category candidates. And this was the cutoff rank for Environmental Engineering.
However this is based on previous years' data and this year it might change. You can predict your college through our Jee Main College Predictor tool

Hi, To get admission in the institute, candidates have to appear in JEE Main exam and participate in JAC Delhi counselling process. Candidates must note that the DTU Delhi reserve 85% for Delhi region candidates and 15% for Outside Delhi region. The cut of DU, DTU is:0-27702 home state in BTech biotech and 0-6595 outside Delhi. For CS- 0- 5k rank for home candidate and 0-2k for outside Delhi, electrical-0-22k home state and 0-4k outside Delhi, IT-0-7k for home state and 0-1916 for outside Delhi.

In order to secure admission in NITs through JEE Main, the good score for the same can be around 80-90 percentile, for DU-75 -90 percentile is the requirement.

Hope this helps.