During the Nazi era, he documented the Jewish life in Breslau in his diaries, until he and his family were deported to German-occupied Lithuania and killed.

In his diaries, he documented life under Nazi rule and the subsequent destruction of Breslau's Jewish community, then the third largest in Germany.

[4] Cohn left a record of everyday Jewish life in Germany after 1933, under conditions of gradually increasing economic, social and cultural oppression.

Acknowledging the threat from the Nazi regime in his diaries, he wrote in August 1935: "From now on, I plan to record our Jewish fate more intently; perhaps it will be of interest to later generations".

The review at H-Net noted:[5] It is rare that such perceptive and comprehensive accounts of this time period survive, and Conrads and Kronenberg [the editor and the translator] help fulfill Cohn's desire to inform future generations about his experiences.