Eis a dominant allele for wet earwax and e is a recessive allele for dry earwax. if two individuals with the phenotype of wet earwax marry, and one of their children has the phenotype of dry earwax, what do we know about the parents?

Given 
E dominant allele for wet
e recessive allele for dry

that means
for phenotype wet, the possible genotypes are EE, or Ee, and
for phenotype dry, the only possible genotype is ee.

Therefore we also know that the child who has dry earwax has genotype ee.
Since the child inherits one allele from each parent, therefore each parent must have a recessive allele "e".

If both parents have phenotype wet earwax, they both must be heterozygous for wet/dry earwax, namely Ee.