Based on the level of respect or formality, you can say "Good luck today" in Korean in 3 ways:

• Informal: oneul haeng-un-eul bileo (오늘 행운을 빌어), oneul haeng-un-eul bilgge (오늘 행운을 빌께)
• Formal: oneul haeng-un-eul bileoyo (오늘 행운을 빌어요), oneul haeng-un-eul bilggeyo (오늘 행운을 빌께요), oneul haeng-un-eul bipnida (오늘 행운을 빕니다)
• Very Formal: oneul haeng-un-eul bilgetseupnida (오늘 행운을 빌겠습니다), oneul haeng-un-eul giwon hapnida (오늘 행운을 기원 합니다)