The exercise indicates that is about an autosomal dominant condition, which means that only one copy of the gene is needed for the condition to manifest, that is why there are no carriers in this genealogy.
I-1 and I-2 have the condition, so they can be heterozygous (Hh) or homozygous dominant (HH). We can know which one if we look at their offspring: we can see that one of their children doesn't have the disease (II-7), and for this to be possible, the recessive gene must have been in the parents, so the parents are heterozygous (Hh).