A man with blood group A marries a woman with blood group O and their daughter has blood group O. Is this information enough to tell you which of the traits – blood group A or O – is dominant? Why or why not?

No, this information is not enough. In the ABO blood grouping system the A blood group is always dominant over the O blood group.

In this case the father must have the genotype of AO which resulted in the OO genotype of their daughter.