Based on the level of respect or formality, you can say "Where is he?" in Korean in 3 ways:

• Informal: geu-ga eodi-e itsseo? (그가 어디에 있어?)
• Formal: geu-ga eodi-e itsseoyo? (그가 어디에 있어요?)
• Very formal: geu-bun-i eodi-e itsseumnikka? (그분이 어디에 있어요?)