It's a interrogative sentence, because it is asking a question.
The way to tell what type of sentence you are reading is to simply check the punctuation. If it has an exclamation mark, then you know it is an exclamatory sentence. If it has a question mark or the sentence features a question, then it is an interrogative sentence. If the sentence is declaring or claiming something, then it is a declarative sentence. If a sentence is commanding something or someone, then it is an imperative sentence.
Hope this helps and have a nice day.
-Kaikai Kitan