What were the effects of Kaiser Wilhelm II on German nationalism?

Here's a few books you might find useful which discuss Kaiser Wilhelm and his rule:

John C. G. Röhl, The Kaiser and His Court: Wilhelm II and the Government of Germany (1994)

Hans-Ulrich Wehler, The German Empire, 1871-1918 (1985)

Various, The Oxford Handbook of Modern German History, especially the chapters by Pieter M. Judson (Nationalism in the Era of the Nation State, 1870–1945) and Helmut Walser-Smith (Authoritarian State, Dynamic Society, Failed Imperialist Power, 1878–1914)

If you don't have access to these then let me know and I can try and find some more accessible texts or a few quotes for you.

With regards to Wilhelm's role at the start of the war compared to at the end, we can see a drastic shift in public opinion of the Kaiser and his effect on morale and support for the war effort. When war broke out in 1914, it was the Kaiser as Commander-in-Chief of the armed forces who gave the order to mobilise. There was an upsurge in patriotic support, and crowds assembled singing and cheering on the Wilhelmstrasse. In the Reichstag, which had long been bitterly divided between the traditional parties of the establishment, and the SPD, a tentative peace was concluded. The Kaiser declared "I know no parties, only Germans". The SPD were willing to give their support to war related laws in exchange for their acceptance by the establishment. However, most of those celebrating were middle class, and mostly male. The surge of excitement at the outbreak of war has been taken by some to indicate that all of Germany came together as one under the Kaiser, but there is little evidence that this is the case, and many germans seem to have been less than pleased about the outbreak of war.

The Kaiser was unquestionably the head of the armed forces according to the constitution, and within a few days was at the front. However the Generals of the German army resented having the inexperienced Wilhelm as their commander, and he was quickly sideline. "The General staff tells me absolutely nothing and also asks me nothing", he complained, "I drink tea, cut wood and go for walks." However, in order to continue patriotic support for the war, the General Staff and Reichstag kept up the illusion that the Kaiser was in command.

If we move forward to 1917-8, the situation has completely changed. The Kaiser's sidelining has been completed by Generals Hindenburg and Ludendorff, who had replaced Erich von Falkenhayn as Chiefs of the General Staff. The two ran what is called the silent dictatorship, where they dictated both domestic and military policy. Chancellor Bethmann-Hollweg was replaced with Georg Michaelis and later Georg von Hertling, both of whom were seen as puppets of the military command. The populace, tired from four long years of war and increasing food shortages, became ever more sceptical of the Kaiser and increasingly war weary. One popular joke went: "Who else will survive the war with all six sons alive", a reference to the Kaiser's many sons, all of whom survived the war unharmed.

It's fair to say that Kaiser Wilhelm as a symbolic figurehead was very important for German nationalism and unity at the start of the war. However, as the war continued and war weariness increased, his status as symbolic figurehead meant that all of Germanys frustration was concentrated in him. While the start of the war was one of the defining moments of the Hohenzollern monarchy, it was also the beginning of its downfall.

I hope this helped, please let me know if you have any more questions.