The recommended option for people who live further from the campus or plan to travel frequently is the “Navegante Metropolitano” monthly subscription, which covers the entire Lisbon metropolitan area and includes all public transportation means (train, subway/metro, tram, bus, and boat). This subscription costs 40€ per month or 30€ for people who are 23-years old and under. You must present proof of enrolment (in a specific template) for this discount to apply and you can request this next to the Academic Services or Life At Nova SBE (in person).
A Lisboa VIVA card is necessary to use this subscription. Cards can be acquired at any station (of any means of transportation), and they cost 7€ (or 3,5€ for students who are 23-years old and under).
There are other options available for people living closer to the campus or who generally travel less. Additional information on different public transportation subscriptions and tickets can be checked here – Price of CP passes multi-operator and intermodal passes | CP.