If you receive $20000 worth of w2g for online blackjack winnings over $1200 and only win $2000 total at the end. How do you report that on your taxes?

Was "$2000 total at the end" in one day?  Or is that over the course of more than one day?

$20,000 or 2,000? You said both.

$2000 at the end.   Lost $18000 of the $20000 worth of wg2. All in 1 “session”.   Can you use the session method in bjack. I know a few years ago they tried to implement Gross Income defined which I am not sure went through. This is online BJ that is why the W2G

So where does the $1200 you mentioned come from?

Yes, you can use the "session" reporting.  So if it was all at one game, one location, and one day, you will report a net of $2000, which will show up on Line 21 of Schedule 1.

However, the IRS computer will expect to see $20,000.  So you will enter $20,000, but counter-act that by a negative $18,000, so the final result on Line 21 will be $2000.  Somebody else can help you figure out how to do that in TurboTax.

As a side note, you mentioned the $1200 threshold for issuing a W-2G.  You need to keep in mind that you need to report ALL session-wins, not only ones that show up on a W-2G.  The session-losses will be an Itemized Deduction on Schedule A, as Critter mentioned below.