How and where do I enter option assignments a) the original short option transaction b) the purchase of the assigned stocks c) selling the stocks ?

You do not have to report the original short option transaction, nor the purchase of the assigned stocks.  The only thing you have to report is the sale of the assigned stock.  You report it like any other stock sale. The only difference is, if you were selling put options and the stock was assigned, your cost basis is the price you paid less the option premium you received. When you sell the stock, you report that cost basis.  Your broker dealer should adjust your cost basis and report the sales on your Form 1099-B.

To enter:

• Type "Investment sales" in the search window and click Enter
• Click on "Jump to Investment sales"
• On the page with "Did you sell any investments in 2018?"  Answer Yes
• Answer Yes to "Did you get a 1099-B..."
• Continue to enter your trades