As part of their 2015-16 State of the Future report (the 18th edition), The Millennium Project conducted a Future Work/Technology 2050 study. Using a Real-Time Delphi survey, the Project asked a panel of 300 experts the following question:

If socio-political-economic systems stay the same around the world, and if technological acceleration, integration, and globalization continue, what percent of the world do you estimate could be unemployed—as we understand being employed today—during each of the following years: 2020; 2030; 2040; 2050?

Their response:

The full chapter (including the responses to 9 other questions also asked of the expert panel) are available here:
Jerome C. Glenn, Elizabeth Florescu, et al. 2015. “Future Work/Technology 2050” in 2015-16 State of the Future.

The Executive Summary for the 2015-16 “State of the Future” report is here:
Jerome C. Glenn, Elizabeth Florescu, et al. 2015. “Executive Summary” in 2015-16 State of the Future.