My sister, Marijke The-Wertheim wrote about her violin lessons from 
Szymon Goldberg in the Japanese Internment Camp Kramat.

At the exhibition ‘Selamat Sjabbat’ at the Jewish Historical Museum in Amsterdam about Jews in the former Dutch East Indies, a significant proportion of the objects on display come from internment camps that the Japanese occupation power set up for the Dutch population during World War II.

Within those camps the Japanese separated Jewish Dutch citizens from all the other prisoners. Among them several musicians were imprisoned who happened to stay in the Dutch East Indies at the moment the occupation took place, i.e. violinist Szimon Goldberg and pianist Lily Kraus.

A number of books extensively describe how Jewish musicians ended up in Japanese internment camps.

Stranded in the Dutch East Indies, music and cabaret in captivity (Gestrand in Indië, muziek en cabaret in gevangenschap (Nadet Somers and Frans Schreuder, Publisher Walburgpers, 2005) on music in captivity.

A thread of fear (Een draad van angst) (Theo Wilton van Reede and Arjan Onder den Wijngaard, Publisher Nijgh & Van Ditmar,1984) about women’s internment camps on Java.

Four turning points in our existence: Dutch East Indies lost, Indonesia born (Vier wendingen in ons bestaan: Indië verloren, Indonesië geboren) (Wim and Hetty Wertheim, Publisher De Geus 1991, the parents of Marijke and her sister Anne-Ruth).
My sister Marijke The-Wertheim writes in 2015:

I personally had violin lessons every day for three months from Szymon Goldberg, at first outside the camp and later, after being interned in the same camp as my father at first, he was moved to Camp Kramat where we were. He was housed with his wife in a separate part of the camp for married couples and families. We were held in the part of the camp for women only. The two parts of the camp were separated by barbed wire.

I had to crawl under the barbed wire to go to my violin lessons. The first time I did this I was caught by a Japanese guard and taken back to the Gatehouse. I was scared to death. In one of the rooms in the Gatehouse, I was made to play Japanese songs on my violin, while they accompanied me on the piano with one finger. Afterwards, they gave me a bag of sweets, which I took ‘home’ (that was a single room which our family shared with another family). My mother had warned us never to eat sweets from the Japs because they might contain poison. But they never bothered me again after the first time and let me crawl under the barbed wire every day for three months! And we ate all the sweets too!

After three months, Szymon Goldberg was sent back to one of many men’s camps, which happened to be the same camp my father was in and he told him all about it!

In the meantime, my sister Anne-Ruth had a few piano lessons from Lily Kraus. She and Goldberg shared the same house in the mixed part of the camp. In order to play piano, Lily Kraus had to come to our part of the camp, where there was a grand piano in the old Pawnshop Building. That was a large empty building with lots of rooms in the middle of a field where we had roll call twice a day. But she did not always get to play the piano as sometimes she was given the key and sometimes she was not.
A concert was to be held in which she and Goldberg were meant to perform, but it was cancelled because the Jews were sent away. First Szymon Goldberg and his wife were sent away, and then we were too.

At an earlier date, I was also meant to perform with Fons Seijler, who also had piano lessons from Lily Kraus, at a concert in the Pawnshop Building, but that did not go ahead either because Fons was taken away, together with all the boys over the age of ten.