Japanese people would have been aware of the German surrender. According to Shillony, Japanese press coverage of the war in Europe was more open than that of the war in Asia. Newspapers printed both the German and the Soviet accounts (Japan was not at war with the Soviets until the end.) There were at least a few Japanese reporters in the Soviet Union, and their accounts were sometimes published, although the overall coverage was of course pro-German. Japanese people read eyewitness accounts of the bombing of the Japanese embassy in Berlin in January 1944. People who cared were pretty well informed about the European war.

Japanese impressions of the war were mostly based on what the press and government said about the war in Asia, and Europe was something of a sideshow. If you read the Japanese diaries collected in Yamashita, there are a few mentions of the German surrender, but it is downplayed by the press. The German surrender was seen as regrettable, but Japanese surrender was unthinkable. When Italy surrendered the papers reported that Mussolini had established a “North Italy”, and thus the three-country alliance was still in place. The diarist mentions that increasingly people had to read between the lines of stories like this to figure out what was really happening. Mostly people paid attention to the events going on around them, and the news of the Asian battles where their relatives might be fighting. The obviously bad news from the Pacific (if nothing else you could track where the battles were happening on the map and figure out that Japan was losing), the direct bombing of Japan (harder to lie about), and lack of food (ditto) and other direct problems were far more important to Japanese than whatever Germany was doing.

Sources

Shillony, Ben-Ami. Politics and Culture in Wartime Japan. Oxford : New York, Oxford: Clarendon Press ; Oxford University Press, Clarendon, 1981.

Yamashita, Samuel Hideo. Leaves from an Autumn of Emergencies: Selections from the Wartime Diaries of Ordinary Japanese. Honolulu: University of Hawaii Press, 2005.