Mrs. And Mr. Smith both have widow’s peaks (dominant). Their first child also has a widow’s peak, but their se?

You didn't finish the question. If the second child doesn't have a widow's peak it means both parents were heterozygous dominant so if you do a Punnet Square you see that there's a 1/4 chance the offspring will not have a widow's peak. They both have to have a recessive allele (lowercase letter) and since they both have widow's peaks they both have Ww (just using a random letter).