I sold stock that my deceased husband received as a bonus each year. I received a 1099-B. I doesn't say anything about cost basis. How can I find this?

In general, if you inherited the stock from your husband, the cost basis will be the market price of the stock on the date of his death.  

You can generally find this information online by looking at historical data for the stock in question.  Or, the brokerage who provided you with the Form 1099-B may be able to help you with the market price of the date of death.

For other ways to find the market price, take a look at the following TurboTax article:  How do I find a stock's cost basis?