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

• Informal: jikeop-i mwo-ya? (직업이 뭐야?), jikeop-i mwo-ni? (직업이 뭐니?)
• Formal: jikeop-i mwo-yeho? (직업이 뭐예요?), jikeop-i mwoet-ipnigga? (직업이 무엇입니까?)
• Very Formal: jikeop-i mwoet-ipnigga? (직업이 무엇입니까?)

- what (objective): mwo (뭐), mueot (무엇), mueot-eul (무엇을), mwol (뭘)
- you (subjective): neo-neun (너는), dangsin-eun (당신은), dansin-ggeseo-neun (당신께서는), ne-ga (네가), ni-ga (니가)
- to do: hada (하다)

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