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

• Informal: hangugeo hal jul ala? (한국어 할줄알아?)
• Formal: hangugeo hal jul aseyo? (한국어 할 줄 아세요?)
• Very formal: hangugeo hasil jul asibmnikka? (한국어 하실줄 아십니까?)