Answer:
The answer is pragmatics.
Explanation:
Pragmatics is the level of linguistics studies that concerns meaning based on context. It's the other side of semantics, which studies the pure meaning in a given language.
In the example, you should have a minimum of pragmatic competence to understand its true meaning (i.e. the opposite of what's really said), because it depends, among other things, on the time, place and the way it is uttered.
