dress is 洋裝 or 連身裙 or 連衣裙，裙子 means skirt
Why does this sentence require the measure word 条？We are not addressing a. quantity. It wouldn't be correct to write 你的条裙子 would it? So why say 这条裙子？
"this" is 这+mw. Normally you might not think about it if you use 这个, but maybe think of it as 这(一)个 "this one ..."