The other person is incorrect! The answer would be “A trait that, if present, is always expressed”.
Yes there can be genotypes with both dominant alleles, but there can also be genotypes with one dominant allele and one recessive that still make the phenotype dominant.
Example:
R = Black Hair (Dominant)
r = Red Hair (Recessive)
RR = Black Hair (Homozygous)
Rr = Black Hair (Heterozygous)
