Still, "You do not have a skirt, George?" would work if we already knew that George doesn't have a skirt and we found the fact unbelievable: "What, you don't have a skirt? You must be kidding me!". Not sure the Arabic translation would be as in the exercise, though.
There are thousands upon thousands of reports, across thousands of sentences, and most of them are useless (99% of reports are spam, abuse, typos that would have been accepted if correctly spelled, just plain wrong, questions that there's no way to answer from the Incubator, bug reports that the contributors can't do anything about, etc.). It takes a lot of time to sort through the useless ones to find a particular good report.
The most helpful thing to do is to report the answer using the button in the lesson, and not comment in the discussion.
That would also work. "Laysa" is a verb, though it is a defective one, not capable of being conjugated in the non-past for example. Now there are situations where the verb doesn't have to agree with the feminine subject in gender, and one of those is if the feminine subject is only grammatically feminine and not biologically so (which a skirt definitely isn't), AND there is another word separating the verb from its subject (which عندك does in this sentence). If these two criteria are met at once, it's only optional for the verb to get conjugated for the feminine. This rule normally applies more in Classical Arabic than MSA, but with "laysa," since it is so often separated from its subject, it kind of stuck through the ages, and people actually prefer to use the masculine in this situation nowadays.