1. What does it mean?
관종 shortens 관심종자. It describes someone perceived as doing things mainly to attract notice, though people sometimes jokingly apply it to their own love of the spotlight.
Also written or said as gwanjong
2. The nuance
It can belittle someone and is not a psychological diagnosis. Posting confidently, enjoying performance, or asking for support does not by itself justify calling a person 관종.
3. Examples
“사진 찍을 때 앞에 나서는 내 모습을 보고 관종 같다고 농담했어.”
I joked that I looked like an attention-seeker because I kept stepping forward for photos.
“도움 요청한 사람을 관종이라고 단정하지 마.”
Don't dismiss someone asking for help as an attention-seeker.
Sources
References support the meaning and usage. Example sentences are written for NoCapWiki.