Based on the level of respect or formality, you can say "What do you do for a living?" in Korean in 3 ways:

• Informal: jigub-i mueoya? (직업이 뭐야?)
• Formal: jigub-i eoddeoke dwoiseyo? (직업이 어떻게 되세요?)
• Very formal: jigub-i eoddeoke dwoisibnikka? (직업이 어떻게 되십니까?)