On a 1099-B I have a stock which when acquired was a PTP, no date acquired, no cost basis. How to proceed?

You likely have been reporting the PTP K-1 since the investment was purchased.  You will have to review your records to obtain date acquired, purchase price and other information.

If the PTP K-1 is being reported annually, the record of the sale could occur through the K-1 screens or through the IRS form 1099-B entry screens.  You would not report both.

Be aware that if:

• At the screen Describe the Partnership, you report Disposed of a portion of my interest.... and
• At the screen Tell Us About Your Sale you reported Sold Partnership Interest,

the sale is being reported.  You would not report the sale on IRS Form 1099-B Proceeds.

Within the K-1 entries,

• at the screen Describe the Partnership, select This partnership ended in 2024, and 
• at the screen Describe Partnership Disposal, select No entry.

In this case, you would report the sale on IRS Form 1099-B Proceeds.

Review the sale of the investment reported on IRS Form 8949 Sales and Other Dispositions of Capital Assets and IRS Form 1040 Schedule D Capital Gains and Losses.

You are able to view the entries at Tax Tools / Print Center / Print, save or preview this year's return.