When studying law there will often be times when a homework question proves difficult and students must seek out additional sources to find an answer. Some students may ask their parents, others may ask a tutor or a more experienced student, and others may ask online. There is nothing inherently wrong with asking about questions about homework online if it is in the interest of expanding on one's knowledge.
Asking assignment questions designed to assess student's abilities however should be discouraged and any question that is obviously for an assignment (e.g. a scanned assignment sheet is posted) should be closed.