Question

A NIC would have most of its population in which economic sector

Answer 1

An "NIC" is a newly industrialized country.  So as the country is ramping up industry, you can expect that most of its population will be employed in the manufacturing sector of the economy.  Newly industrialized countries see a shift away from an agriculturally based system to an industry based system.  So they also see a large measure of urbanization as people move away from rural areas and into cities for jobs in industry/manufacturing.