Hi , I am on J1 visa in US. I have a NRE bank account in India through which I pay my mortgage on a home loan I have taken from an Indian bank. I don't own any home in US. Do I have to report all this to IRS. How does it work? Thanks

As long as you are a non-resident alien under the J-1 visa, you have no requirement to report ANY Indian asset to the U.S. government.