Why do we not use article before noun fruit in this question?
Do you like fruit?
The fact that the sentence is a question is not relevant. We would use a zero article (that is, no article, definite or indefinite) in a statement also: I like fruit, Jack likes fruit, we like fruit, my stove burns coal, my dog eats meat.
We use the zero article before a mass (uncountable) noun. 'Fruit' here is a mass noun.
The same is true when the noun is plural but of indefinite number: the boy loves to play with toys.
We do not use an article for a general assertion or question. So, when asking “Do you like fruit?” this is a general question that could mean any type of fruit. The answer could be “Yes, I like fruit. My favorite fruit is watermelon.” On the other hand, if you were to present a bowl of fruit to a dinner guest, while they are eating you can “Do you like the/this/that fruit?” since you are referring to a specific bowl/piece of fruit that is in front of you. The answer could be “Yeah, this fruit is very fresh and sweet!”
“Do you like blueberries?” is a general question while inquiring about someone’s preferences, but on the other hand “Do you like these blueberries?” would be appropriate when asking about a specific container of blueberries that you are serving to someone. (if these specific ones are too soft, firm, sour, sweet, etc)