I had a mole removed. Does the wound heal better covered with a band aid or uncovered?

Depends. It is important to keep wounds clean and moist to facilitate healing. Topical antibiotic ointment, with or without coverage with a bandage, is sometimes prescribed. Make sure the scar is not exposed to significant sunlight to avoid darkening the scar. Follow up with the physician who removed the mole.
Oncovered generally. Once the area has granulation tissue and a scab is forming, or if you had stitches, and the area is clean, "opening it to air" with often promote faster healing. Occluding with a band aid is important at first to keep dirt out of the area to avoid infection though. Topical antibioitc creams are also recommended for wound healing and infection control. Good luck.