Below are the K-pop "Big 4" stocks. Before investing, please consult with a financial advisor about regulations and market risks. If you are a foreigner that lives outside of South Korea, then you may need a brokerage account to have access to KOSDAQ or KRX.
HYBE https://www.google.com/finance/quote/352820:KRX
SM Entertainment https://www.google.com/finance/quote/041510:KOSDAQ
JYP Entertainment https://www.google.com/finance/quote/035900:KOSDAQ
YG Entertainment(INVEST HERE IF YOU LOVE BabyMonster!) https://www.google.com/finance/quote/122870:KOSDAQ