In context, they usually mean the same thing. There is a difference that I shall illustrate for you. "CAN you speak Chinese" = Are you ABLE to speak Chinese? Is it something that you are able to do? "DO you speak Chinese" = Do you speak Chinese REGULARLY? [eg. to friends, in work, etc.] Of course, to actually speak Chinese to your friends, you have to be ABLE to speak it. Similarly, to be ABLE to speak Chinese, you generally need to have spoken it before... [But not necessarily....] The two are relatively interchangeable but I'm sure you can see the difference. ----- The rule is true in other sentence structures: "CAN you play golf?" = Are you ABLE to play golf? Is it something you're able to do? "DO you play golf?" = Do you play golf with your friends? Is that something you do on a regular basis? ---- I hope you can see the difference and, moreover, I hope this helps!

They are essentially asking the same thing. They're both grammatically correct.