Based on the level of respect or formality, you can say "Can I have a discount?" in Korean in 3 ways:

• Informal: kkaga jul-rae? (깍아 줄래?)
• Formal: kkaga jul-raeyo? (깍아 줄래요?)
• Very formal: kkaga jusil su itsseumnikka? (깍아 주시겠습니까?)