Final answer:
Ms. Hart taught Law at her alma mater, the John Marshall Law School in Chicago, and was known for her work in social justice and advocacy.
Step-by-step explanation:
The subject Ms. Hart taught is Law. Pearl M. Hart was a pioneering figure who, after earning her law degree from the John Marshall Law School in Chicago, made her mark as the first woman lawyer to practice criminal law in the city. She was deeply invested in social justice, defending those most vulnerable in society. Ms. Hart taught law at her alma mater, imparting legal education and extending her advocacy into the classroom. Her commitment was not just to teach law, but also to provide pro bono services to causes she believed in and to actively support social justice groups.