Hi there!

So this question could easily pertain to the other major combatants of WW1, not just Germany. The short answer to this is: most of the great European powers thought of the Russo-Japanese War as an amateur affair. They widely recognized at the time Russia had a weak monarchy and lots of internal turmoil. The Japanese, so they assumed (largely under racist pretenses) that they wouldn't ever be able to match the sophistication of European style armies. The long answer was: European general staffs were looking for ways to capture operational mobility again after what they had seen as decades of indecisive battles. The Russo-Japanese War offered them more of the same without any particularly new innovations. I think this is how you should frame an approach to this question.

It must also be remembered that no large-scale war had been fought in Europe since the Franco-Prussian War of 1870-71, and the military and technological advances that had advanced since went untested.

To get where we want to go, let's briefly look at how combat had developed in the latter-half of the 19th century and the problems associated with the tactical and operational art at that time.

The Problem

Armies had never been larger. Troops had never been better trained or equipped, and there was a plethora of intelligent minds contributing to military doctrine. However, there was a problem generals could see all over the world. There were bigger, badder, more destructive battles being fought (Italian Wars of unification, Austro-Prussian and Franco-Prussian Wars, the American Civil War) and yet these great confrontations were indecisive. They didn't produce Napoleonic style epic defeats (take your pick) where one decisive battle could end the conflict. No. The defeated army would retreat, and the victorious army would not pursue.

Largely this was due to the advancement of technology. Rifled guns, increased ranges and sizes of artillery meant higher casualties for defender and attacker alike.

The typical arm of combat used to pursue, cavalry, was being used less and less as a method of pursuit. Now, because you could reload a rifle faster and shoot the bullet farther, and you had an 8 or 9 foot target to aim at (horse and rider), cavalry forces became easier targets even for a retreating enemy to pick off.

Russo-Japanese War

So what did this war have to offer in terms of solutions for operational mobility? What problems did the war present for its combatants?

In short, the war clearly demonstrated the interrelated problems of fire, maneuver, and command of large armies with modern equipment in battlefield conditions. Both sides found their operations severely limited by supply, and both had a very tenuous supply line. For Japan, they had to transport supplies across the sea. For the Russians, they had a 5,000 mile supply line to maintain.

The Japanese began the war with a surprise attack on the Russian 1st Pacific Squadron in Port Arthur. On February 16, 1904 the Japanese began landing in Korea.

I won't detail the entire war, but let's choose one battle, see how it went, and see what kinds of lessons Europeans derived from it.

The Battle of Liaoyang

After the Japanese landed and had assaulted Russian positions on the Yalu River, the chief of the Japanese GEneral Staff, Marshal Iwao Oyama, was now in the theater and acting as supreme commander. He, like many other generals in the Japanese army, were influence by former Prussian General Helmuth von Moltke. Briefly, Moltke believed in Auftragstatik (or mission tactics). He did not deliver long detailed orders. Rather, he gave an objective to his subordinates, the time and place when they should be there by, and let his subordinates do the rest. This allowed for tactical flexibility and often, ingenuity on the part of lower ranking officers. In RJW, Oyama and his chief of staff, General Gentaro Kodama constructed a framework: a concentric advance by all available Japanese armies wouold fix the Russian main body in place, then destroy it. The exact shape of the climactic battle would only be decidede when the Russian deployment became clear. The hope was to create a Kesselschlacht (or literally, cauldron battle) to encircle and destroy the Russian army.

Well, the Russians didn't cooperate. Near Liaoyang, the Russian army under Kuropatkin dug three concentric rings of defensive works around the city, making the Japanese advance slow and costly. The battle raged for 10 tens, almost unheard of in previous military history (aside from the Battle of Spotsylvania). Kuropatkin proved a capable general. Each time the Japanese moved to flank him, he would reposition his forces to meet the threat with interior lines. Over time the Japanese gradually pulled the Russians back, as the latter's train supply line was threatened by Japanese forces. However, the Russians retreated in good order. The battle cost the Japanese 23,000 men to the Russians 17,000. The Japanese took no Russian guns.

Another issue with the Japanese pursuing the Russians was the size of the battlefield. Russian earthworks stretched for over 50 miles. It was nearly impossible to continuously coordinate attacking forces on a front that large for any period length of time.

Lessons

The battle of Liaoyang and other engagements did lead to some lessons, but these were not heeded by European observers in meaningful ways (as we see at the onset of WW1).

1. Artillery had become the dominant arm on the batlefield. IT dictated where and when assaults could succeed and defenders could hold.
2. Cavalry had become increasingly worthless on the attack, was of little use even on the defense, and in fact was no longer even particularly effective as a flank guard or security force.
3. Infantry could prosecute a successful assault if it was given proper support (especially artillery)

Overall, the BIG takeaway (as we see with German obsession to achieve swift victory and the French concept of elan they assumed would carry the day in WW1) was that the advantage went to the side that attacked, who kept attacking, and was sufficiently strong-willed to accept the inevitable losses caused by modern weaponry.

To tie this to the Germans (but really more broadly to most European powers at the time) So it's not that we need to find new tactics to break through the enemy. We have the weaponry and excellent training. What we need to instill in the men is that they need to be fearless, accept the inevitable losses that will occur through this type of battle, and we'll win.

Sources

Connaughton, Richard. Rising Sun and Tumbling Bear: Russia's war with China.

Citino, Robert M. Quest for Decisive Victory: From Stalemate to Blitzkrieg in Europe, 1899-1940