The daughter walks up to her father and asks him, "Dad, can I ask you something?"
The father says, "Of course, what's your question?"
The daughter replies and asks, "How do you feel about abortion?"
The father says, "Why don't you ask your sister?"
The daughter replies, "I don't have a sis-"
Alright listen up, buttercup. The joke is that the daughter asks her dad about abortion, and the dad suggests she ask her sister. The punchline is that she doesn't HAVE a sister, implying the daughter was aborted. Basically, the joke is dark because it suggests a failed abortion. You are probably pro-choice so you like the joke, even though you are dumb.
