SSI is needs based, and gambling winnings can impact that.
"What percentage do I receive for turning someone in..." Sounds like OP is tryign to cash in.
If a person is collecting SSI, they are required to report all of their income to the Social Security Administration, including gambling winnings. If you know the person is not doing that, you would report it to the Social Security Administration.
I could be wrong, but as far as I know, they don't offer a reward to you for reporting that.
Call the IRS: 1-800-829-1040 hours 7 AM - 7 PM local time Monday-Friday
<a rel="nofollow" target="_blank" href="https://oig.ssa.gov/report">https://oig.ssa.gov/report</a>