There's no single answer to how many distinctions are needed to graduate cum laude in a humanities faculty. The requirements vary significantly from university to university, and sometimes even between departments within a single university. Some universities may use a GPA system, others a weighted grading system, and still others may have specific requirements for honors courses or theses.
To find the answer, you must consult the specific graduation requirements of the humanities faculty at the university in question. This information is typically found on the university's website, often in the academic regulations or undergraduate catalog.