My percentile in Jan 2020 JEE Mains is 99.03. Will I be able to get admission in CS in NSIT, DTU or IIITD? My father is an ex-service man. Will I get, if required, any benefit for that?

Hello Praveen, if you got 99.03 percentile in JEE Main then your rank after JEE Main April will be around 10 thousand based on this percentile.
Last year closing Cutoff rank for Netaji Subas University of technology (NSIT) Delhi, Delhi Technological University (DTU) and Indraprastha Institute of Information technology(IIIT) Delhi are

NSIT Delhi

Home state General candidate
Computer Engineering - 4343
Computer Science with specialisation in Artificial intelligence - 3454

All India Quota
Computer Engineering - 1849
Computer Science with specialisation in artificial intelligence - 1336


DTU

Home state
Computer Engineering - 8852

All India
Computer Engineering - 2866


IIIT Delhi

Home state
Computer Science and Applied Mathematics - 25271
Computer Science and Artificial intelligence - 10439

All India Quota
Computer Science and applied Mathematics - 6442
Computer Science and artificial intelligence - 3793

As you you are son of ex service man then it will surely benefits you as there is a special quota for Defence personal in all these colleges which includes ward of ex serviceman also.