If you owe taxes, will the irs garnish your winnings?

You betcha. Remember what the Beatles said about the UK's Inland Revenue, which is the equivalent of the American IRS: When you die, "They'll tax the pennies on your eyes."

Unless it is something like a lotto jackpot IRS will be unlikely to know about your winnings until it receives a W-2G from the casino so except maybe lotto, no.

How much and from whom?  If you win over a certain amount from a casino, they will withhold some for taxes and pay the IRS for your account.  They do that for everyone and they have no idea you owe the IRS money.

If you win $17 from a dog track, you are good.

The IRS can put a tax lien on your property, seize money from a bank account, garnish your wages and so forth.  They did the first 2 to me.  They thought I owed them a lot. In fact, I owed them very little. But I had not filed in years.  So I did my back taxes and I got a refund of nearly everything they confiscated from that bank account. (A large amount)

I hired a CPA and we asked for a hearing so they would not keep seizing other accounts in the meantime. Some collections rep wanted me to send them an extra $2000 a month until we finished and I said sure. My fear was the forced sale of all my stocks.

All in all, while the confiscating money and the tax lien scared me, after I got a CPA and did my back taxes, the IRS is not that hard to deal with. The huge refund was automatic.  And I got any evidence of the tax lien removed from my credit. It knocked my score down by like 90 points.  But then went back up when it was removed.

The irs can do anything they want