gambling winnings

I'll be intentionally vague about some things. Someone I know won $300,000 online gambling with a VPN. I believe they said they used a Mexico address. They live in California. Paid out in etherum. How should they figure tax? How would you even classify the income. Can you even claim online gambling winnings? Are there any trusted online sources to look at? I was afraid it was a scam but they've cashed out some into USD already. I'm not really looking for tax advice, more looking for trustworthy resources that I can learn from. . . . Editing to achieve proper letter count. why you would force someone to just keep typing when there's no text counter (that I know about) is beyond me.