This example is a question or interrogative sentence and so I do not think the term "simple subject' applies. However, if it has a subject, "what" is it.
"It can." In that sentence, the pronoun "it" is the simple subject.
The simple subject of the sentence is "you".
"Natives" is the simple subject.
A simple subject is a thing. If it were talking about a Baseball or a sentence the baseball is the simple subject.
The simple subject in the sentence "Did you find your wallet" is "you."
The simple subject in the sentence is "Cherokee."
we
Plane is the simple subject.
The simple subject is "rehearsals." The simple subject is one word that will directly answer the question Who? or What?
"Cherokee" is the simple subject in that sentence.
the simple subject of a sentence is what the sentence is in one word
"The dog" is a noun phrase that serves as the subject of a sentence, but it is not a complete sentence by itself. A simple sentence requires both a subject and a predicate, such as "The dog barks." In this case, "the dog" functions as the subject of the simple sentence.