Who is the 'he', the doctor or somebody else?
Even as the doctor was recommending rest, HE knew that this in itself was not enough, that one could never get real rest without a peaceful mind.

Does "HE" denote the doctor or the patient whom the doctor give advice to according to the context of the above sentence?

Question

Who is the 'he', the doctor or somebody else?
Even as the doctor was recommending rest, HE knew that this in itself was not enough, that one could never get real rest without a peaceful mind.

Does "HE" denote the doctor or the patient whom the doctor give advice to according to the context of the above sentence?

Answer

Probably ,but can't tell without additional info. 
Could be either the doctor or the patient.

Answer

I can't give you the answer without the preceding sentences.