What was Pavel's previous occupation before coming to the concentration camp?

Pavel is an elderly Jewish man who had been banned from practicing medicine during the war, under the Anti-Semitic laws of the Nazi government. Under Nazi law, the medical licenses of Jewish physicians were cancelled in 1938. The novel takes place in 1942, during the height of power held by Germany and its allies during the Second World War.
When Bruno falls off the swing and injures himself, Pavel attends to his wounds and assures the boy he will not need stitches. Bruno questions this and tells Pavel he is not a doctor. Readers are not informed where the man comes from, or what discipline of medicine he is in, only that he was a physician:

I certainly am a doctor. Just because a man glances up at the sky at night does not make him an astronomer, you know.

Bruno’s childish logic is as follows: Pavel is a waiter for the commandant at "Out-With"; therefore he cannot be a doctor. Bruno is largely unaware of the circumstances Jews have been placed under during the war; he is naïve to the fact that thousands upon thousands of Jews were forced to give up their occupations to serve the Nazis. Pavel’s response conveys the idea that appearances are not all that they seem.
https://encyclopedia.ushmm.org/content/en/article/antisemitic-legislation-1933-1939

In Chapter 7, Bruno falls from a tire swing, and Pavel rushes out of the house to help him. Pavel carries Bruno inside and cleans the wound on Bruno's knee. Pavel assures Bruno that he will be okay and puts a bandage over his cut. Bruno then comments to Pavel that his mother might want to take him to the doctor just in case. Again, Pavel assures Bruno that he will be alright. Bruno doesn't believe Pavel and says, "You're not a doctor" (Boyne 82). Pavel responds by saying, "Yes I am" (Boyne 82). Bruno does not understand how Pavel can be both a waiter and a doctor, but Pavel insists that he was a doctor. Bruno is naive and does not understand that Pavel was a doctor before he came to the concentration camp. Bruno then asks Pavel why he is peeling vegetables when he should be working in a hospital. Pavel tells Bruno that before he came to "Out-With" he practiced as a doctor. Before Pavel can begin to elaborate on his past life, Bruno's mother walks in the kitchen and their conversation ends.