1099-B stock sale. I have a catetory X with no cost basis. There is no select for category X, just A - F. How do I report my sale using Turbo Tax?

You can use category (box) E. 

Reference: https://ttlc.intuit.com/community/business-taxes/discussion/how-do-i-find-the-sale-category-on-my-1099-b-form/00/731225

You'll want to enter an individual transaction instead a summary transaction.  When you enter individual transactions, you will have the sales category X as an option.  Make sure you enter both date acquired and date sold to calculate the correct holding period.