In principle, you should know the cost basis of the stocks you owned, as you became the owner by acquisition, inheritance or gift.
If you do not know or remember the cost basis, you should do some research to find it or make an educated guess for it, otherwise the whole proceeds will be taxable as capital gains.
I'm totally confused about how to report it. Is this considered employee stock? It doesn't seem to fit the definitions offered in TurboTax. And I did not receive anything from my company detailing the cost basis of the stock that they transferred from my 401K to the investment company's IRA. This stock was the company contribution in my 401K. So far my company doesn't have an answer--they said I should have it but I don't remember getting anything like that when I retired. Thank you for any help you can offer!
Please clarify.
You said the stock was transferred from your 401(k) to the investment company's IRA. Is the IRA in your name?
If that stock was sold within the IRA, then the form 1099-B is issued in the name of the IRA, not your personal name. In this case, you do not report it on your tax return.
To follow-up on the comments from @MinhT1, it does not appear as if you have anything to report because the stock was transferred from your 401(k) to your individual retirement account (IRA). When you withdraw funds from your IRA, you will get a 1099-R, and you will report your 1099-R on your tax return. Some of the income on your 1099-R may not be taxable, but TurboTax will help you figure out how much tax is due.