Montagne Sainte-Geneviève, a hill on the left bank of the Seine, was the site of the College of La Marche, where Calvin went to school when he was 14. The building was demolished during the Second Empire, so there really isn't anything to see, but pickings are probably going to be slim in Paris. It's near the Pantheon.
His second school in Paris was the College de Montaigu. It was, I think, located at the Place de la Pantheon on the corner of Rue des Sept-Voies (now named Rue Valette - one street west of Rue de la Montagne Sainte- Genevieve) Again, I don't think the building has survived. But if you go to the Pantheon and look back toward the River and Notre Dame then pan to the right, you will be looking a the right general area for both schools.