In the parking lot behind the mosque. Directions here:
http://www.masjidalhikmahnewyork.org/ (not the V train, though; that doesn't run on weekends).
Suggestions: get there early, maybe by about 12, so you can sit on the sidewalk in the shade on the west side of the mosque. In the afternoon, the shade goes away.
Be courteous and hand over your money with your right hand.
This thread has some specific food suggestions:
I'll try to take notes and issue a detailed report next week.