An amazing place to eat some local dishes and have some quality beer is Meierei. Situated in the New Garden of Potsdam it's just a short walk from the Cecilienhof palace, this is a working brewery with a nice indoor restaurant and a fantastic beer garden just by the river.
If it's sunny outside you should really go for the beer garden even thou it might be packed with locals. The bratwurst goes very well with mustard, fries and that tasty fresh beer. Since the view is amazing and the beer is so good you might want to spend some time in this relaxing place so make sure you don't spend all day walking in the gardens of the Potsdam palaces.