。
Is it true that Midori is good at the violin?
Literal
Midori [topic-は] violin [subject-が] skilled [quotative-というの-は] truth [question-ですか].
Note 緑 could be a proper name here — 'Midori' is a common Japanese given name from the word for green. The sentence pattern ~というのは本当ですか ('is it true that X?') is a standard 'confirm hearsay' question. 上手 ('skilled at') takes が on the skill or activity, like 好き does — another adjective whose 'object' is grammatically the subject.