Online comments keep giving one big tax percentage like it settles everything. For an Indian resident with a valid US prize there may be US withholding, final US tax and Indian reporting. Where can a person read the official starting points before speaking with a cross-border tax professional?
They are separate tax steps. For a nonresident alien, the IRS generally applies 30% US withholding to gross US gambling winnings unless a treaty exemption applies. India is not among the gambling-income exemptions listed in the current IRS guidance. The payer normally reports the prize and withholding on Form 1042-S.
For an Indian tax resident, current Income Tax Department return material lists lottery winnings under section 115BB at a 30% special rate, before any applicable surcharge and cess. The Indian return also has foreign-income and treaty/foreign-tax-credit reporting. Do not simply add the two headline rates: whether US tax can be credited in India depends on the facts and documentation. Keep the ticket, claim statement and 1042-S, and use an adviser who handles both US nonresident and Indian resident returns.