we can't see the K-1 or 1099-B. normally the K-1 would only report your share of the S-Corp income/loss for the current period and not your sale of the S-Corp stock (especially so since it was not the S-Corp that bought it). the 1099-B needs to be entered in the 1040 because the IRS gets a copy (it also gets a copy of the k-1). your tax basis might or might not be the same as the proceeds. the 1040 form 8949 is supposed to reflect your tax basis. since it wasn't supplied you are going to need to determine it. it is highly unlikely that you have no gain or loss from the sale of the stock.
1099B
From a previous post in Intuit – We put the cost basis to be equal to the proceeds so that the 1099B would show zero gain. don't where you saw this but in your situation, it is highly unlikely this is correct. since you got a 1099-B that's where the sale price and cost are supposed to be reported not through the k-1 disposition worksheet.
