Answer and Explanation:
A character sketch, as the name suggests, is a type of draft or summary of a character. In this case, we are analyzing a character that belongs to an existing story. However, character sketches are often used by authors before they begin to write the story as a means to build their characters. It usually concerns physical appearance, personality, actions, and feelings, among other possibilities. Since the story you chose is "Condensed Milk", we will be sketching the narrator/main character, whose name is not revealed.
Character sketch:
The narrator is a man, an adult, probably an intellectual. He is mentally exhausted and physically sick. He can only care about his own surviving for the moment, even though he is still able to empathize. No matter how empty he feels, he is still witty and determined enough to escape danger and take some slight advantage of a dire situation.
Evidence for the sketch above:
The narrator is a man, an adult, probably an intellectual. - "There was no reason for us politicals to be there..."
He is mentally exhausted and physically sick. - "Inside there was only an empty scorched sensation, and we were indifferent to everything, making plans no further than the next day." "I rolled up my pants and showed the breaks in the skin from scurvy."
He can only care about his own surviving for the moment, even though he is still able to empathize. No matter how empty he feels, he is still witty and determined enough to escape danger and take some slight advantage of a dire situation. - "It was, of course, a weak, worthless act of vengeance just like all my feelings. But what else could I do? Warn the others? I didn’t know them. But they needed a warning."