You can find the position of the Department of Physics at this link
From Geneva, the best way to reach Milano is to use the direct trains, there are four of them each day and they take a little over 4 hours to travel from Geneva Cornavin to Milano Central Stations. To reach the department from the Central Station you can take the green metro line to Piola and then walk 10 minutes, as shown here
If you come by airplane, you will land in one of the three airports serving Milano.
Linate (LIN) is the closest, from there you can take the blue metro line to the city center; this route shows how to get to the Department directly from Linate airport. You can also take a taxi that would cost some 10-20 euro.
From Malpensa (MXP) there are trains to Milano Porta Garibaldi and buses to Milano Cantral Station, while from Bergamo/Orio Al Serio airport, there are buses to Milano Central Station. The buses are quite frequent (every 10-15 minutes) and take 1 hour; the trains run twice every hour and also take 1 hour. Porta Garibaldi and Central Station are both on the green metro line, which you can take to reach the Department (see "From Geneva" directions above). You can also take a taxi from the bus/train arrival to the Department (10-20 euros), while taking a taxi directly from the airports would be considerably more expensive (50-100 euros).
You can find here information on the public transport in Milano, and a map of the metro to download.
Bus and metro fares can be bought with a contactless credit card at the metro entrance and on the buses. For the metro you will need to swipe your card (or phone, watch, etc) at the exit too. The airport bus fares can be bought when boarding the bus, while the train ticket from Malpensa can be bought at the vending machine at the station entrance.
