From Beijing to Nanjing, you can choose to take D trains, which takes only about 8hrs. The D trains are departing at Beijing south train station and the ticket price for one soft seat is around CNY343. From the capital airport to south train station, you can take the airport bus to Xidan station first and then take a taxi. From Nanjing train station, you can take a taxi to the Nanjing University directly, which is about 12km away.