Based on the level of respect or formality, you can say "Have you been to South Korea?" in Korean in 3 ways:

• Informal: hanguk-e ga-bon jeok itni? (한국에 가본 적 있니?), hanguk-e ga-bon jeok itseo? (한국에 가본 적 있어?)
• Formal: hanguk-e ga-bon jeok itnayo? (한국에 가본 적 있나요?), hanguk-e ga-bon jeok itseupnigga? (한국에 가본 적 있습니까?)
• Very Formal: hanguk-e ga-bo-sin jeok itseusipnigga? (한국에 가신적 있으십니까?) 한국에 가셨던적 있으십니까?

- you (subjective): neo (너), neo-neun (너는), dangsin-eun (당신은), dansin-ggeseo-neun (당신께서는)
- to have been to [where]: [eodi-e] ga-bon jeok itda ([어디에] 가본 적 있다)
- South Korea: nam han (남한), hanguk (한국)

Please refer to How to pronounce Korean Alphabet for the English pronunciation in this answer.