1. What food do you like most?
2. Which food do you llike the most?
3. What kind of food do you like best?
4. What kinds of food do you like the best?
(Are all the expressions grammatical?)
All are grammatical, and all are commonly used.
#2 is asking "which" of some specifically named foods you like most, but the others are inviting the listener to supply his/her own favorites.
All of the expressions you provided are grammatically correct. However, there are slight differences in meaning and usage.
1. "What food do you like most?" - This sentence is asking about your favorite food in general, without specifying any specific category or type. It could be any kind of food.
2. "Which food do you like the most?" - This sentence assumes that the person asking the question has provided you with a specific set of options or choices to choose from. You are being asked to select the food you like the most from that given set.
3. "What kind of food do you like best?" - This question is asking about your favorite type or category of food. It implies that you have a preference for a particular cuisine or style of cooking.
4. "What kinds of food do you like the best?" - This sentence is similar to the third one but uses the plural form, suggesting that you enjoy multiple types or categories of food.
In summary, all the expressions are grammatically correct, but they have different nuances in terms of the specificity of the question and the range of food choices being considered.