From Duolingo:
Questions – Do you have, Do you own?

• Oes car gyda chi? – Do you have a car?
• Oes car gynnoch chi?
• Oes gynnoch chi gar?
• Oes gen ti gath? – Do you have a cat?
• Oes cath gydag Owen? – Does Owen have a cat?
• Oes ganddyn nhw gath? – Do they have a cat?
  
• Oes – yes
• Nac oes – no
• Oes gan Olwen gath? – Does Olwen have a cat?
• Nac oes, mae gynni hi ddau gi. – No, she has two dogs