both

Both are correct. With the second sentence, you have a more specific thing that you want help with. The first question is a more open question.

"Could" is more polite. "Can" is used with family and friends (but not usually coworkers). "Could you do me a favor?" is usually followed by some details. Example: "Could you do me a favor? I need a ride to the airport on Monday." "Could you do this favor for me?" usually follows the description of "this" favor. "I need a ride to the airport on Monday. Could you do this (favor) for me?" Often, "favor" is omitted.