How should I report a cryptocurrency margin trade where my assets got completely liquidated?

You would report the transaction the same way you would report the sale of stock, a bond, or any other security.  In this regard, you would enter your basis (cost), proceeds, and the resulting gain or loss.  You will also need to enter the dates of your purchase and the date of sale so TurboTax can calculate whether your gain or loss was short term or long term.

Because you were on margin, the margin expense would be added to your basis as a way to adjust your basis to reflect your true cost of owning the Ethereum.  

You did not indicate whether you have a document you intend to upload into TurboTax for the transaction in question.  Nevertheless, the easiest and fastest way to get your crypto transactions into TurboTax is by using the import method. If you’d rather download a CSV file from your crypto service and upload it to TurboTax, here’s how.

1. Sign in to TurboTax, and open or continue your return
2. In the Wages and Income section under Investments and Savings (or Investment Income), select Start or Revisit next to Crypto (1099-B)
3. On the next screen, you may see Did you sell any of these investments in 2021? or Time to kick off your investments!, select either Yes or Okay!
4. On the We can make this faster screen, select Enter a different way, and then select Cryptocurrency on the following screen
   1. If, instead, you’re asked to select an investment type, select Cryptocurrency
   2. You’ll then see the Get ready to be impressed screen. Select Continue, then select Try another way
5. Select Upload on the Select your crypto experience screen 
6. On the What’s the name of the crypto service you used screen, select your crypto service from the dropdown menu 
7. After downloading your CSV file from your crypto service, upload it on the Go ahead and upload your crypto CSV file screen 
   1. Note: Make sure your file extension is .csv
8. Review your uploaded crypto information

TurboTax supports CSV files uploaded from these cryptocurrency services.

• Bitcoin.Tax
• BitTaxer
• Coinbase
• CoinTracker
• CoinLedger
• Robinhood
• TokenTax