Tactics of World War I were quite well known by staff officers, as generally the situations were fairly well understood in the early war era. Officers of this era were normally conservative thinkers in terms of military tactics, and as such many of these doctrinal tactics were older and had been demonstrated prior to the wars early stages. In fact, it was this understanding and antiquating of tactics that combined with the technological advancements of many nations armed forces that contributed to WWIs massive casualties. As the war progressed, so did technology, and new tactics arose from this. Doctrines and tactics shifted slightly and adapted and were often quickly countered or met with an opposing contemporary. The late war tactics and technological advances would lay the groundwork for most of the tactics seen in World War II.

In WWII tactics had changed and indeed were ever changing. Germnay unleased the concept of Combined Arms on the world at a schale never before truly matched. Combined Arms being the integration of all elements into war: armor, artillery, aircraft, infantry and so forth. It was by and large a shock to its opponents, mostly because of them feigning ignorance. There was, in the major allies command, a gold understanding of the axis tactics, and vice versa. The United States even had a training film made concerning Japanese infantry battalion stricture and how best to maximize ability against it. However, as the war went on, more and more tactics changed. The surprise of the Germans by the astonishing integration of Armor to Soviet infantry units (and damned good armor too), the deployment of fallschirmjäger against Crete and the reaction of the allies therein, the shocking speed at which the Americans adapted to combating Japanese Aircraft are all relatively good examples of generally failing to recognize shifts in tactics and doctrines of the enemy.

TL;DR in the beginning, quite a bit. In the actual wartime era, it shifted around as tactics changed, but remained a decent level of understanding.