If you are in the Investments section (under Wages & Income), and you went into the 'Stocks, Mutual Funds...' topic, you are asked on the next screen if you received a 1099-B, then you are asked for the name of your Financial Institution.
If you didn't visit these areas, but only indicated at the beginning of the TurboTax interview that you 'sold stocks', don't worry. Unless you actually get into this area and enter something, it won't affect your return.