Where does an “Ethnomusicologist” find a job?
Literally any university that has a music program. It's not like they're going to be able to do anything with practical value in larger society.
As to the song's origins. There are only so many notes in the range that the typical human voice can sing. Pretty much every melody and chord progression that is pleasing to the ear has already been sung, put to paper, recorded, and re-worked/stolen again and again. Even Bach and Handel were notorious thieves of other composer's music.