At which point in time did the majority of German population become aware of the Holocaust?

I would go along with the view that the full horrors and industrial scale of the Shoah were not clearly known by the civilian populace in wartime Germany nor, for that matter, did the Allied leaders and their Army top brass fully comprehend or grasp the enormity of this situation during the war, that is not until the post-1945 era.

I would venture my own answer to the OP by informing of my attendance at a lecture in 1993 given by the distinguished historian Thomas Otte, currently Professor of History at the University of East Anglia in the UK. In response to my question about Daniel Goldhagen's controversial book, Hitler's Willing Executioners, the young Dr. Otte, as he then was, offered what I can only take as an informed opinion that the great urban populations of Germany must have wondered about the fate that awaited Germany's Jews as they disappeared in greater and greater numbers from the towns and cities in 1942-1945. When pressed to expand on his opinion, Dr. Otte added a rider that the great German urban populations "turned their heads away" in a wave of collective indifference as their cities and towns became Judenrein. I subsequently learned that Thomas Otte earned his PhD at the University of Birmingham in the UK, having first taken all the glittering prizes in his undergraduate days at the University of Heidelberg. Professor Otte is German and speaks English without a trace of a "foreign" accent.

Edit: the late Professor Jan Karski, the Polish patriot and distinguished academic, was smuggled into the Warsaw ghetto and saw for himself how hundreds and thousands of Jews were being systematically starved to death by the German Army in occupation. He made his way to the UK and US during the war to alert the Allied leaders of this and the other activities at German extermination camps on Polish soil. His reports to the Allies were not acted upon. (see Claude Lanzmann's 9-hour documentary & various books of the late Prof. Jan Karski)

Are there autobiographies from ordinary German citizens about the time of the war, containing information about their level of awareness of the Holocaust's proceedings and scale?

The earliest mention of the atrocities that I have found is in a book titled "Kreuzzug gegen das Christentum" by Franz Zürcher, published 1938 in Switzerland (Europa-Verlag). This book was translated to French and Polish.

In addition to the other excellent answers, I would like to mention the Posen Conference of October 6, 1943. Its express purpose was to make sure that the Nazi leadership (Reichleiters and Gauleiters) could not claim ignorance of the Final Solution - and, being aware of the determination of the allies to prosecute war crimes, will fight harder.

This is not, of course, "the majority of German population", but it is still an important data point: in the fall of 1943, when the extermination programs have been in full swing for over two years, the top party officials might still be able to deny knowing about it.

I think you have some false assumptions, namely that "large numbers" of soldiers were involved in the holocaust, which is not true. Early in the war there were "einsatzgruppen" which had a few thousand, but these were disbanded or repurposed over time and most of the holocaust took place in great secrecy. All of the death camps, with the exception of Auschwitz-Birkenau, were located in remote locations and run by very small squads of men under the the direct control of Adolph Eichmann, who reported to Himmler. The execution areas in Auschwitz, which were located in the Birkenau area of the camp, were carefully segregated from the main parts of the camp and every effort was made to make Auschwitz look like nothing other than a work camp.

Before the war started there were no death camps, and all of the camps were publicized as work camps. Letters were allowed in out and the conditions were made relatively public.

After the war started, news concerning the camps was gradually decreased until the public received no information whatsoever, and most Germans and foreigners simply assumed the camps were no different than they were before the war. The death camps like Chelmo, Treblinka and Majdanek, were constructed in militarily controlled areas in complete secrecy. Noone even knew they existed except those immediately involved in their operations. Locals were removed for miles around the death camps, which were placed in remote areas to begin with.

The full dimensions of the holocaust did not become clear until the war was over and research gradually revealed the nature and extent of it. Even during the trials at Nuremberg, the prosecutors did not fully know of the existence of the death camps or understand how they were used, except Auschwitz. For example, a large number of prisoners escaped from Sobibor and could theoretically have testified to its existence, but nevertheless no major trial took place until 1965 and only 6 Germans were convicted. The total number of Germans involved at Sobibor was perhaps a few dozen at most.

In the immediate aftermath of the war, the Holocaust was represented by the emaciated corpses discovered at Dachau of which newsreels were taken, however, Dachau was not even a death camp. The prisoners died from starvation and cholera near the end of the war after food and water supplies were cut off.

In the years after the war 1945-1949, the German public was "re-educated" to become aware of the Holocaust, but the focus of "education" was on well-known aspects such as the camps in the western sectors such as Dachau, Buchenwald and on the use of slave labor in the factories, and on what was known of Auschwitz, which was limited because it had been destroyed and was in the Soviet sector. For this reason the full scope of the exterminations only gradually became clear, both to the Germans and the world at large, over the course of the 1950s and 1960s. In 1954, Gregory Frumkin writing in Switzerland, published a statistical book in which he tallied 6 million Jews as having disappeared from eastern Europe based on census data, and this was widely misinterpreted as a death count and publicized in that way. From the date though (1954) you can see that scope of the Holocaust was something that was revealed not all at once, but over time.

Tyler Durden's answer is excellent. But you request autobiographical evidence from Germans writing during the war. One German of note is the diarist Victor Klemperer. As a highly educated Jewish professor Klemperer was very far from representative of the general German population. However it is telling that his information (and he, understandably, took a keen interest in all such news) about the fate of fellow Jews was patchy.

He writes about "evacuations" to the east and about work camps, rather than death camps. He well knew that the camps would be terrible places for even home in Germany his life was reduced to humiliating work duties, poor food and other privations. Certainly there were rumours of shootings, but his diaries suggest that rumours of all kinds were in circulation, some more and some less believable. In 1942 he mentions hearing about a "dreadful" camp at Auschwitz. But even Klemperer writing after the war is astonished to learn that Jews had been systematically killed in their millions.

Klemperer's wartimes diaries come in two volumes: I Will Bear Witness and To The Bitter End.