Rikers is a jail which means it houses three groups. Those are pretrial detainee, people convicted of misdemeanors (crimes punishable by up to a year), or people convicted of felonies (crimes punishable by more than a year) but who were sentenced to less than a year.
If he is sentenced to incarceration for over a year, Trump would go to one of New York's prisons. If under a year, he could go to a jail like Rikers.