I am sorry to hear about this concern for Keno.
A chronic scratch could suggest a underlying allergy problem. Environmental allergies are quite common for both dogs and cats. Other considerations could include mange (mites), a ear infection, or other contact allergy.
So, definitely, this is well worth a vet visit, since Keno is scratching enough that hair loss is prominent. Even in the absence of any irritation, crusting, or moist discharge, it could progress quickly.
A vet might suggest a oral steroid or a steroid shot to get the itching under control and maybe a simple skin test or two to ensure no infection or mange concern.
But, we definitely can't resolve this with at home therapies, so the vet visit is well worth it.
Antihistamines would be one consideration, but I am doubtful that giving a 1/4 to a 1/2 tablet of benadryl 25mg antihistamine will help.
Hope that information helps