This is a textbook question.
A man with blood group "A" marries a woman with blood group "O". Their daughter is having blood Group "O". Is this information enough to tell which blood group is dominan
Blood Group Variations
No, this information is not enough.
During a cross breeding, even recessive traits can express themselves phenotypically, in case, heterozygous chromosome mate with each other. If AO mates with OO, then there is probability of the child inheriting OO genotype. So you cannot determine the dominant blood group here.