In the sentence what did you have for dinner?

Question

Is have a linking verb?
Is the word what an adverb, a direct object, or an indirect object?

Answer 1

Is have a linking verb?

http://grammar.yourdictionary.com/parts-of-speech/verbs/Linking-Verbs.html

Is the word what an adverb, a direct object, or an indirect object?

Subject: you
Verb: did have
Prepositional phrase: for dinner

Answer 2

Still confused
I am thinking a direct object?

Answer 3

You are right! What is the direct object in this sentence! :-)