Jaffna food is Tamil: rice, string hoppers, pittu, dosa, curries with coconut and tamarind, and a lot of seafood. Jaffna crab curry and the seafood soup known as kool are local specialities, and palmyra treacle with curd is a typical sweet. Meat and fish are common, so vegetarians should choose their restaurants rather than rely on menus.
We could verify three listings from a travel guide. Malayan Cafe and Akshathai (Nila) are described as vegetarian, and Mangos is described as an Indian restaurant for dosa and kotthu parotta. We could not confirm that either vegetarian restaurant is strictly Pure Veg, so neither carries a diet tag; ask about egg on arrival. We found no verified Jain kitchen, and no vegan restaurant. For Jain or no-onion meals, ask your hotel to arrange them in advance and carry snacks.
In practice, order dosa, idli, vada, vegetable thali and rice with dhal and vegetable curries, and ask whether dishes contain egg, fish stock or dried fish. Drink bottled or filtered water.