Based on the level of respect or formality, you can say "Are you closed?" in Korean in 3 ways:

• Informal: ggeutnatseo? (끝났어?), ggeutnatji? (끝났지?)
• Formal: ggeutnatseoyo? (끝났어요?), ggeutnatseupnigga? (끝나습니까?)
• Very Formal: ggeutnasieotseupnigga? (끝나셨습니까?)

- you (subjective): neo (너), neo-neun (너는), dangsin-eun (당신은), dansin-ggeseo-neun (당신께서는) - omitted here
- to close: ggeutnada (끝나다), datda (닫다)

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