Where to report my capital loss from selling stock?

You should have a 1099-B from your broker. Enter that into TurboTax. 

If you did not receive a 1099-B for this stock sale, you can still enter the stock sale in your return. 

• Click on the Wages & Income tab
• Next click on I'll choose what I work on
• Scroll down the screen until you come to the section Investment Income
• Chose Stocks, Mutual Funds, Bonds, Other and select Start or Update
• The first screen will ask if you sold any investments during the year, answer 
• Did you get a 1099-B or a brokerage statement for these sales? Answer No
• Tell us about this sale, Click I'll enter one sale at a time
• The drop-down boxes can be filled out with the details of the stock sale
• Enter if this was short-term or long-term
• Enter the type of investment

1. Date sold - your records
2. Date acquired - from your records
3. Sale proceeds -your records
4. Cost basis - your records