1042-S is just the same as a 1099 but generally issued to nonresident aliens with backup withholding or without withholding due to treaty or IRC applications.  It could also be issued to a US person who did not certify his/her US status.

You would report the income on the usual forms/schedules/lines, depending on the type of income it is.  You will be able to identify the type of income it is based on the income code by referring to the table on the form.

Where is the 1042-S income reported on the 1040NR.  The client received a stipend, and the institution has issued a 1042-S with Gross Income and Federal Tax Withheld