cost basis for sale of stocks

Sorry for your loss. Value at date of death.

If the stocks were only in his name at the time of his death, then your cost basis in the stocks is likely the fair market value of the stocks on the date of death.

There are websites which can tell you the stock price on a given date.

IRS Publication 551, page 10, here states:

The basis of property inherited from a decedent is generally one of the following.

1. The fair market value (FMV) of the property at the date of the individual's death.
2. The fair market value (FMV) on the alternate valuation date if the personal representative for the estate chooses to use alternate valuation. 
3. The value under the special-use valuation method for real property used in farming or a closely held business if chosen for estate tax purposes. 
4. The decedent's adjusted basis in land to the extent of the value excluded from the decedent's taxable estate as a qualified conservation easement.

To post the sale of stocks, follow these steps:

• Click on Federal down the left side of the screen.
• Click on Wages & Income down the left side of the screen.
• Scroll down to Investments and Savings and click the down arrow to the right.
• Click Start / Revisit to the right of Stocks, Cryptocurrency, Mutual Funds, Bonds, Other.
• Click Add investments.

Sorry for your loss.