if a dragon born is attacked for horns or their scales, will both grow back or will horn damage be permanent??
horn damage tends to be more permanent --- regrowth is possible, but would take decades to regenerate, and even then it will almost never return to the same size it was before. it could go unnoticed if the damage wasn't too severe, but if a dragonborn were to lose a whole half of their horn for example, any regrowth would be very slow (potentially more than a century) and the horn's growth would be stunted.
scales are easier to regrow, by virtue of being part of the dragonborn's "skin," but could still take months or years to completely regenerate if the wound wasn't too grave. again, for more severe cases, it could take much longer and even leave scars / affect the pattern of growing scales in that part of the dragonborn's body. however, assuming that the dragonborn remains healthy, their self-regeneration will gradually cause those scars to fade over time.
i do personally love a little drama in the form of scars & damaged horns though, so i'll say it's possible for injuries to seem permanent if the initial trauma was severe enough, just because they would take so long to heal!