It's generally best to add salt to the batter before frying. This ensures even distribution of flavor throughout the food.
Adding salt to the batter before frying allows the salt to dissolve and distribute evenly throughout the mixture. This results in a more consistent and flavorful end product. When salt is added after frying, it tends to sit on the surface and may not penetrate the food properly, leading to uneven seasoning. Furthermore, salt draws moisture out of food. If you add salt after frying, it can make the fried item soggy more quickly. By incorporating the salt into the batter, you're essentially seasoning the food from the inside out. This is especially important for thicker batters or foods that take longer to fry, as it ensures the interior is adequately seasoned. Consider the type of salt you are using as well. Finer salts, like table salt, will dissolve more readily than coarser salts, like sea salt, so adjust accordingly.
Be mindful of the amount of salt you add to the batter. It's always easier to add more salt later (although less effective) than to remove it. Start with a small amount and taste the batter before frying to ensure it's seasoned to your liking.