Nanjing has a relatively wide selection of local foods called Jin Su cuisine, along with restaurants featuring Chinese cuisine from other provinces and foreign restaurants. The prices are lower than in Shanghai. You can find both Chinese and Western food.
A local favorite is Yanshui Ya (salted and baked duck), and you can see the ducks hanging in shops and restaurants. Another local dish is Eight Delicacies Soup made of fish, water chestnuts, lotus root, parsley, arrowroot, lotus seeds and other ingredients. This is a popular dish especially around "Moon Festival" time. A good place to go for Nanjing cuisine and Chinese cuisine is the area around Confucius Temple and the Qinhuai River.
If you want to have a western meal, then there are western style restaurants serving the expats and students on Shanghai Lu that is a street near universities.