Anybody vs. Nobody

'Anybody' is a non-assertive indefinite pronoun. When we use 'body' (or any words formed by the prefix 'any') we are not sure (asserted) of the existence of a thing/person. We are referring to a random person out of an indefinite number of persons without holding any specific presuppositions in our minds.

In interrogative sentences, when we want to genuinely ask questions about a person and we are seeking an answer, we use non-assertive indefinite pronouns. Because we do not the existence of a thing/person. This is the normal (or unmarked) way of asking questions in English.

Typically, negative sentences usually take non-assertive forms. It is the normal (or unmarked) way of a negative sentence.

'Nobody' is a negative indefinite pronoun. It shows absence of a person. Note that when we have 'nobody' in a sentence, the verb should not be in negative form, because negative pronouns have the ability to make a sentence negative. They do not any help.

We cannot use negative words in questions.

Negative words are inherently negative, which is why they do not need another negative marker in a sentence.