ghaj means "to have" as in "to possess" or "to own". Are you saying that you interpret this English sentence as meaning that you possess the actual ridges that were on your father's forehead? Should we be limited to teaching only sentences that can be translated literally and directly with no euphemism or colloquialism? Surely part of our task is to teach you when direct literal translation doesn't work and how to interpret the meaning behind a phrase from one language to another. I sympathize with you that it is the most difficult part of learning a new language and that the Duolingo platform is not ideal for this kind of subtlety, but rather than a trap, please see it as an opportunity to learn how expressions differ between the languages.
There is a noun suffix -Hom which means "minor" which is introduced near the end of the course, but there is no noun ??vIl??. There is a verb vIl which means "to be ridgy/have ridges". Perhaps there is a noun we don't know about or which has fallen out of use that means, "a ridge". Then vIlHom could mean something like, "minor ridges". However, that is just speculation and you should instead take vIlHom as a complete word that can't be broken down and which is solely used to refer to the ridges on a forehead.