Question on how to enter cost basis for 1099 DIV Box 9

It depends. If you have reduced your cost basis in the stock to zero then all of it is taxable, if not then none of it is taxable. Putting $0 in the cost basis box will not change your tax return and should allow you to proceed.

As indicated in the 'Learn More' link the taxable amount would go under Investment Income (Stocks, bonds, mutual funds, other, then select Other) as a sale with the taxable amount as the gross proceeds and zero cost basis (if you have no basis or you do not know your basis/cost). Long or short term depends on the holding period.

• Long term is a holding period of more than one year and receives capital gain tax treatment (0%, 10%, 15%, 20% depending on your regular rate of tax)
• Short term is a holding period of one year or less and receives ordinary gain tax treatment (your regular rate)

Enter your transaction here.

1. Open (continue) your return if it isn't already open.
2. In TurboTax, search (upper right) > Type 1099B  Press enter > then select the Jump to link 
3. Answer Yes to Did you sell stocks, mutual funds, bonds, or other investments in 2023?
   • If you see Here's the info we have for these investment sales, select Add More Sales.
4. Answer NO to Did you get a 1099-B or brokerage statement for these sales?  
5. Follow the instructions.