Complex sentence: Demographer Sergio DellaPergola proposed an "extended" Jewish population, including people identifying as partly Jewish and non-Jews with Jewish parents, that numbered 17.3 million globally, and an "enlarged" Jewish population figure that also included non-Jewish members of Jewish households and totals 20.2 million.
Split into simpler sentences: Demographer Sergio DellaPergola proposed an "extended" Jewish population, including people identifying as partly Jewish and non-Jews with Jewish parents, that numbers 17.3 million globally. His "enlarged" Jewish population figure further includes non-Jewish members of Jewish households and totals 20.2 million.