Both "how about you?" and "what about you?" are correct ways to ask the same question back to the other person. They are idiomatic expressions used to ask someone for their opinion or response. There is a slight difference between them, and the choice depends on the speaker and their judgment of the situation. Here are some general guidelines:

• Use "how about you?" to ask about feelings, emotions, or anything personal.
• Use "what about you?" to prompt discussion, gather information, or encourage participation.
• Both phrases are often interchangeable.
• "How about you?" can be used to make a suggestion or express empathy.
• "What about you?" can be used to mention an objection or a potential problem.

In summary, both phrases are correct and can be used interchangeably in most conversations. The choice between them depends on the context and the speakers intention.