I would suggest visiting la Grande Mosquée de Paris- it is absolutely beautiful. It isn't too far from Gare du Nord, about 5.5 km, but taking the métro is very easy.
Otherwise, there is La Mosquée El Fath, Mosquée Abou Bakr, or Mosquée Khalid Ibn Walid. I would recommend searching on Google or using http://fr.mappy.com/for these mosques to see which one is closest to where you will be staying.