Share holders were credited for the co. sale of foreign rights July of 2018. My 1099-B short term has no "cost" just a gain. How do I get Turbo Tax to accept this gain?

You might be able to allocate some of your stock's basis to the rights you sold; check whatever prospectus/proxy/etc. that the company mailed to you when they issued the rights.

I expect that TurboTax doesn't like the fact that you (apparently) left the basis box blank.  Put a "0" in there and the problem will go away.

Tom Young