The Blackstone Group LP reorganized from a partnership to a corporation. Therefore, on the K-1 questions, I should check "This partnership ended in 2019", correct?

Yes. That is the final partnership return.

Ok, checked the box, this gives an error where TT wants the cost and sales price. Since there was no GL, I entered 0 cost and sales price, the error went away. Another approach was to uncheck the box. How should this be approached?

What you did will be fine for tax purposes.  There should not be any gain or loss on this entity structure change.

Having said that, hopefully you have been maintaining your basis in this investment as this is now your cost basis in the corporation.  Make sure you keep this information.

If you haven't maintained a basis schedule, you need to get this pulled together sooner rather than later as the longer you put this off, the more likely it is to lose information in order to determine your basis.

Hi again,

As a follow up, I notice by entering the 0's the tax return shows and ending capital account balance whereas the K-1 has a "-" because it was transferred out as part of the exchange. Should I just ignore that or enter my costs basis and then put the cost basis as the sale price?

Yes.

LOL You meant yes to just ignore and leave 0 as the cost and sales price right?

Hi I know  a little late to the Party but in entering the BX partnership information if I check "partnership ended in 2019" the next screen asks describe disposal? options are no entry, complete disposition, disposition was not via sale and sold and am receiving payments.  Just want to know the right option because depending on what you choose it starts you on the path of when bought, when sold.. - thank you in advance to anyone that has some advice. 

Anybody have any guidance on this? I'm stuck at the same decision point on 'Describe Partnership Disposal'.

there is no gain or loss on the PTP reorganizing to a C-Corp.

from schedule L 

your basis is beginning capital account            say 10000

+

current year net income                                        say  200         

-

from part III amount on 19a distributions     say 500

basis 10000+200-500=9700

now if you sold the C-Corp stock in 2019, your tax basis would need to be computed as above and you would need to substitute that on the 1099-B worksheet not on the disposition section of the k-1