The question you should ask yourself before surveying an essay is: "Why am I reading this essay?" (Option C).
Before surveying an essay, it's important to understand why you are reading it in the first place. This will help you stay focused on the main purpose of the essay and identify the key points that the author is trying to convey. Option A ("Where does the story take place?") is more relevant to a narrative or descriptive essay, while option B ("Why is the author making this point?") is a question that you should ask while reading the essay in detail. Option D ("How long will this take to read?") is not relevant to the purpose of surveying an essay, which is to quickly get an overview of the main ideas and structure.
Hope that helps! Have a nice day! :)