Blackstone Group LP reorganized to a corp. in 2019 and units were exchanged for common stock in the new Blackstone Group Inc. How & where do I report this on my return

Normally, you would receive a form 1099-B from the company if there was a taxable transaction involved. You would report that in the "Investment Income" section of TurboTax, and then "Stocks, Mutual Funds, Bonds and Other."

If there was a taxable gain or loss to be reported, you would report it as an investment sale, by listing your sale amount less the cost basis of the investment.