So, for example, in May 2013 Steve Camarota and Karen Ziegler of CIS reported, based upon U.S. Census Bureau data for 2009 - 2011, that:
Of the 472 civilian occupations, only six are majority immigrant (legal and illegal). These six occupations account for 1 percent of the total U.S. workforce. Moreover, native-born Americans still comprise 46 percent of workers even in these occupations.That's pretty similar to the following claim from three authors at Pew this spring:
Compared with their 5% share of the civilian workforce overall, unauthorized immigrants are overrepresented in farming and construction occupations (26% and 15%, respectively). In all industries and occupations, though, they are outnumbered by U.S.-born workers.The two statements differ slightly because Pew's is restricted to illegal aliens, while CIS's also includes aliens here legally (i.e. lawful permanent residents and "temporary" workers).
[5 facts about illegal immigration in the U.S., by Jens Manuel Krogstad, Jeffrey S. Passel, and D'Vera Cohn, April 27, 2017]
Anyway, when discussing illegal immigration with your generally-clueless fellow citizens, you can assure them, "There are no jobs that American citizens won't do," and cite Pew as your authority.