Loyalty to the country they were living in. German Jews were just as determined to support the nation as were German Christians. The evidence is that a fifth of all Jews served during WW1 in the army – around 100,000, of whom 12,000 were killed and 35,000 were given special awards. In spite of these facts, latent negativity towards Jews lay behind the false rumouring that they were war dodgers. (In October 1916 the German War Minister arranged a statistical survey to check the extent of Jewish war service and those not participating.). Some were Russian Jews, and treated as doubly suspect  - enemy aliens.This had become the basis of propaganda publications already in 1919:
https://www.tabletmag.com/jewish-arts-and-culture/books/248615/jews-who-stabbed-germany-in-the-back
For some portraits of war service by German Jewish artist Hermann Struck:   https://blog.nli.org.il/en/lbh_struck/?utm_source=activetrail&utm_medium=email&utm_campaign=%20English%20Newsletter%2019.03.2020&_atscid=3_2269_202250386_9930555_0_Txtxxft3ajshss2hau8  
Inevitable conflict of German and Austrian Jews with British Jews British Jews were likewise just as determined to support the nation as were British (and French) Christians. There was a shared understanding that whenever Jews found themselves firing ‘blind’, but aware that there might be Jew on the receiving end, they would shout Shema as a warning: https://blog.nli.org.il/en/jewish_germany_army.
Some ambivalence towards service in the German army is recorded This is evident in the personal reflections of an Austrian Jew in the German army at the thought of having to shoot Italian civilians https://blog.nli.org.il/en/memories_of_wwi.
Jewish experience on other war fronts. The same issue arose on other fronts with Jews also in both the Austrian and Russian armies, and in the Middle East Palestinian Jews sided with the British. A strange consequence at the Western Wall is recorded:in Jerusalem: on the first day of Rosh Hashanah Jewish soldiers from the Austrian and German armies prayed there and on the second day of the Festival so did Jews in the British army. https://www.jewishhistory.org/jews-in-wwi;  https://www.myjewishlearning.com/article/wi-and-the-jews. For a history of praying at the Western Wall:https://blog.nli.org.il/en/hoi_western_wall/?_atscid=3_2269_202250386_9967917_0_Txtxxft3ajshss2hau8&utm_source=activetrail&utm_medium=email&utm_campaign=%20English%20Newsletter%2029.07.2020
Response of Martin Buber 
Martin Buber is better known for expounding the notion of I-Thou-ness and more specifically for his promotion of the recreation of Zion even in the decade before WW1. However, his affirmation of being German and Jewish was clearly expressed during the war itself. He was disappointed that his physical health disqualified him from military service and he complained in letters to colleagues outside Germany that the country was being unjustly vilified. One of his correspondents was Frederik van Eeden, a leading Dutch psychiatrist. Here Buber is claiming that Belgian atrocities were not one-sided:
“You and your friends must know that Belgian women amused themselves by putting out the eyes of wounded German soldiers and forcing buttons ripped from their uniforms into the empty sockets. I am not indicting the Belgian people; mine is the task of understanding outraged people, even which they commit crimes against all that is meant by humanity … I am protesting against declarations of Germany’s guilt and the innocence of the others.
I find it reprehensible that there is vilification on the German side too…In our times, it should be part of decent warfare to recognize and acknowledge the enemy’s legitimacy; denigrating the enemy means denigrating one’s own struggle. Still, it is worth noting that the German vilification sounds rather childish in its crudity and lack of rancour, compared with the monstrous flood of slander in the French papers, especially, but also in English periodicals (as far as possible, I read the statements of all the nations involved); these are marked by a zest for lying, a zest for defaming the enemy, that offends my deepest sense of human dignity.” Nahum N Glatzer & Paul Mendes-Flohr (eds) The Letters of Martin Buber. A Life of Dialogue (1996) p 163.