1. What kind of books are you looking for?

2. What kinds of books are you looking for?

(Which one is correct?)

3. What kind of food do you like?
4. What kinds of food do you like?
5. What kinds of foods do you like?
(Which one is correct?)

6. What kind of fruits do you have?
7. What kinds of fruits do you have?
8. What kind of fruit do you have?
(Which one is correct?)

1 & 2 - both are correct.

3 & 4 are correct; 5 is not.

8 is correct; 6 & 7 are not.

I know I'm being picky, but putting plural endings on "fruit" and "food" (which are collective nouns) is unnecessary and incorrect.