Sir i got 499 gate score belongs to obc in ECE in which NIT i will place and which specialisation is good

According to this year's qualifying cut off, you have passed the cutoff. Now, the next step is to identify which colleges you can get with this score.
Admissions to the postgraduate programmes will be through CCMT which is the Centralized Counselling for M.Tech/ M.Arch/ M.Plan admissions at the NITs, and other GFTIs.
According to previous year trends, you can get :

• IIIT Gwalior - VLSI & embedded systems (360 closing marks in 2018 and 410 closing marks in 2017 for OBC NCL category)
• NIT Jalandhar  - ECE ( 370, 423)

VLSI (456, 511)

• MNIT Jaipur - ECE (486,550)

-Embedded systems (433,459)

• IIITDM, Kanchipuram - Communication system design (365, 464)

-Design in electronic systems (474, 464)

• IIEST Shibpur - Signal processing (390,422)

• Check out this article for detailed list of all NITs
• https://www.google.com/amp/s/engineering.careers360.com/articles/gate-cutoff-for-nits
• You should choose a course of your own interest. Think back to your last 4 years in engineering and try to see which papers you were more interested in. If you liked Signal processing, then try for that specialisation. It depends purely on your interest.