Translation:The singer is thin.
Almost! It should be "날싼합니다."
+Might I add that this is a formal sentence, so you would probably attach ~씨 to the name 지민 to make it polite. "지민씨가 날씬합니다" or "지민씨가 날싼해요."
I believe you are referring to Park Jimin from BTS? In that case, it's very common for fans to use honorifics like 오빠 or 형 (if the fan is younger) when talking to idols. So you could say "지민오빠가 날씬해요."