Overall, he is very healthy for a 93 year old. He has some problems moving around, can't hear too good, has a cataract, none of which he wants treated. But this cancer on his head is starting to get infected and smell. He doesn't smell anything bad because he won't take a bath and so he stinks anyway, but that is another question.
You could call your local social services department and explain your dad's situation. They may be able to put you in touch with a home health provider. You could also contact your local area on aging and talk to someone who works with elderly people and understands the difficulties you face in trying to do the best thing for your dad.
I don't see any way you can get him medical care with out making him angry. Is it possible for you to explain that his choices put you in a moral situation that you are not comfortable with?
There is a very wise person on this site. He name is Jeannie Gibbs. I'm going to send her a post and ask her to comment on your situation. She gives great advise.
In the meantime, tell me if your dad has medicare, etc.
You know your dad's history. Has he always been this way. Does he seem of sound mind to you?
Your dad may have a skin cancer that can be treated successfully also. It seems a shame to let it progress. Maybe he can't smell it, but I would think he could feel it.
It seems wise to call your state social services department or area on aging and get some input. You have POA for him and you could call his doctor to get advise. You seem to understand that it is a cancer on his head, so I assume it has been diagnosed?
I respect the right of an elder to not want to take steps to prolong their life, but in your dad's case, I would wonder about his ability to make common sense decisions and the possibility of you being held responsible for letting him go without treatment.
Hopefully, you will get many comments here and they will be more informative that my thoughts.
Ideally, it would be best to take him to his doctor and have some in home care for him. Best wishes, Cattails.