This question is closer to an error in reasoning question than to a true weakness. Either way, we are asked to find the piece of information that is missing, whose absence is a flaw in the argument.
We should start by looking for why the argument is flawed, and then picking an answer choice that best matches our understanding of the flaw. For the argument, the author uses data about people who survived a first heart attack. From this data, the author makes a general claim about all smokers and all nonsmokers. However, the data excludes a set of people from the sample- that is, people who did not survive. The flaw in the argument is therefore that the author makes a general claim about all people based on data that only covers a specific group of people.
This flaw is a fairly close match to answer choice (E). In general for these questions, having a strong understanding of how the argument is flawed is the key.
