Identify the point of view of "The Paperhanger". Who is the telling the story? When is the story told from—before, after, or while these events are occurring? What role does this play in creating, maintaining, or alleviating narrative tension?

The point of view of this story can be described a number of different ways.
The story is told by a third-person omniscient narrator in the past tense. The focus changes throughout the story, beginning with the doctor’s wife, moving to the paperhanger, then to the doctor, and then finally back to the paperhanger. The events of the story have happened in the past but are told in chronological order. It is worth noting that the final revelation of what happened to the child is told as the memory is revisited by a character, not as the omniscient narrator saw it happen.
That the story is told in the past tense creates narrative tension by making it unclear whether the truth of Zeineb’s disappearance will ever be revealed. Because the day that Zeineb disappeared is firmly in the past—the story opens by telling us it “was an event so cataclysmic that it forever divided time into the then and the now, the before and the after”—it is possible for the narrator to return to it at any point in the story; the omniscient narrator knows what happened, and the reader is aware of this. When the narrator moves through different characters’s perspectives, the reader feels anticipation that the character will finally reveal that they are responsible or will reveal what they know.