There are many ways to know the best food destinations of a place,
Internet: The most convenient and effective way is to search in internet. You can go to google and type the keywords to get numerous websites/blogs you can browse through. Here you can get not only the best local foods but also where to get them, the direction of the restaurant/shop from your place along with any other benefits/deals running on the internet only.
Travel Magazine: You can also go through the travel magazines to get the relevant information.
Local People: If you do not rely on the internet or magazines then you can simply go there and ask the local people about the food destinations. They are the best person to guide you.