When using verbs that indicate wearing of clothes or accessories, you should use + 고 있다, instead of -아/어 있다. Therefore, 입고 있는 is the correct form.
긴 치마를 입는 여자가 누구예요? means "Who's that girl putting on a long skirt?"
In other words, she's still in the process of putting a long skirt on, and doesn't have it entirely on yet.
When using verbs that indicate wearing of clothes or accessories, you should use + 고 있다, instead of -아/어 있다. Therefore, 입고 있는 is the correct form.
긴 치마를 입는 여자가 누구예요? means "Who's that girl putting on a long skirt?"
In other words, she's still in the process of putting a long skirt on, and doesn't have it entirely on yet.