What did the average German citizen know about the war?

All one needed was a map of Europe and the German propaganda reports on the fighting (and maybe some pins to mark places).

Official German radio reports about fighting included names of cities that lay in the vicinity of the combat and rivers that were crossed. The reports were heavy with propaganda-speak, blurring losses and denying defeat. But if one filtered out all the phraeseology and just concentrated on the cities that were mentioned, he could get a good overview of the back and forth motion of the general frontlines.

Completely lying about the course of the frontline would have been impossible. Too many men were soldiers, and they went on home leave occasionally. Wikipedia says that approximately 18.000.000 men served in the Wehrmacht [Wikipedia]. It was impossible to prevent them from talking to people at home.

I don't know how the reports differed with respect to information content between radio, on-screen, and the newspapers.

SHORT ANSWER

Ordinary German citizens had access to a range of sources of information despite the attempts of the Nazi party to control this flow. Soldiers returning from the various fronts were one obvious source, the BBC service in German another. From 1943 onward, Allied bombing and increasingly severe rationing were inescapable facts of life for most Germans (though some were in a state of denial).

MORE DETAILED ANSWER

The Nazi party introduced tight controls on the media almost as soon as it assumed power in 1933. The Holocaust Encyclopedia states that

Rather than suppressing news, the Nazi propaganda apparatus instead sought to tightly control its flow and interpretation and to deny access to alternative sources of news.

In effect, when things weren’t going too well, they would just spin it or not report it at all

Despite the Nazi regime’s tight control on all forms of media, it was not difficult for ordinary Germans to get a general idea of how the war was going; those who wanted to could, but it would not have been a very clear picture at times. Soldiers returning from the various fronts told their families and friends, and the BBC news service in German could be received throughout the country. The penalty for listening to it was death but 52% of the people (German Jews and non-Jews who were over 17 years old during the war) Eric A. Johnson & Karl-Heinz Reuband interviewed for their book What We Knew: Terror, Mass Murder, and Everyday Life in Nazi Germany tuned in to the BBC anyway. The BBC had a clear aim:

The BBC wanted its German language service....to become a trusted news source, which meant even defeats had to be truthfully reported.

Despite attempts to jam programmes and prosecute listeners in Germany for tuning into enemy broadcasts, the BBC soon became one of the most significant sources of information for people living under Nazi rule.

There were other sources of information for Germans not inclined to tune in to the BBC. Johnson & Reuband state that information on the mass murder of Jews

…came from so many quarters. Some witnessed it happening or even participated directly in it, and, not infrequently, described it to others. Some heard about it second or third hand – from soldiers on leave from the eastern front, foreign news broadcasts, well-informed friends, relatives, and clergymen, and occasionally Gestapo officers and Nazi Party officials.

If some German citizens were hearing about atrocities against Jews and partisans on the eastern front even in 1941 and 1942, they were certainly hearing about military reverses too. Richard J. Evans, regius professor of modern history at Cambridge University, makes this clear when he states:

In particular the catastrophe of Stalingrad began to convince many Germans that the war could not be won.

Nonetheless, what many ordinary German citizens knew depended on, in part at least, what they wanted to know or believe. One has to remember that those who were still young towards the end of the war had effectively been subjected to Nazi indoctrination since childhood so believing anything other than what the state propaganda machine churned out was far from given, sometimes even in the face substantial evidence. Then there were also those who just shut out all bad news, or who were more concerned about everyday trivial matters (witness: the diary of Brigitte Eicke, a teenager during the war).

By 1943, the allies were bombing German cities heavily: this had happened only sporadically before so it wouldn’t have taken a genius to work out that the Luftwaffe, at least, was not performing as well as it had previously done. Joanna Bourke in The Second World War: a People’s History states that

...by 1943, there was no question that the Allies were in charge of the skies. In that year, British and American air forces dropped over 200,000 tons of bombs on Germany, while the Luftwaffe managed to drop only 2,000 tons of bombs on Britain. The most deadly attack of 1943 was the Battle of Hamburg between late July and early August, when 50,000 civilians were killed, most in a massive firestorm

Of course, this did not go unnoticed in Germany. Writing on the Hamburg raids of July/August 1943, Richard J. Evans states:

Refugees from the devastated city spread a sense of shock and foreboding all across Germany.

In summary, ordinary German citizens could get information (though news of some specific reversals may have taken time to get through) but, for many, knowing and accepting reality were not necessarily the same thing.

Other sources:

Roderick Stackelberg, 'The Routledge Companion to Nazi Germany’ (2007)

German officer interview

Alexander J. De Grand, 'Fascist Italy and Nazi Germany' (1995)

Omer Bartov, 'The Eastern Front, 1941 to 1945'