There is a mareez, for whom diagnosis hasn't helped yet in identifying the actual source of the disease, hence the existing treatments have not been helpful, (for almost 8-10 years now).

1) Given the situation, can we consider the patient with an incurable disease and give khaak e shifa as medicinal treatment. If yes, then how much quantity is allowed in a single dosage

2) How frequently it is permissible to intake.

1) Yes a very small amount mixed with water. http://duas.org/kshifa.htm

2) Only for shifa purposes whenever one wants