Question

How did Germany and Japan treat occupied (conquered) people?

Answer 1

This is a difficult question covering a huge amount of different situations but in general I would say not very well.

Explanation:

The German Army during Second World War was closely followed by special formations of killing squads or Einsatzkommandos, normally from the SS, whose task was to round up Jews, political opponents (komsomol members or commissars in Soviet Union), Roma or Gypsies and either kill them on the spot or send them to concentration camps.
Consider also that Russians in general were considered subhumans and so treated in the worst possible manner; in particular a special plan for Soviet Union called for rational and planned starvation of the population to kill at least 30 millions of Russians (and use the rest as slaves) as it was tried, in smaller scale, during the siege of Leningrad!
Another incredible feature of German invasion of Russia was that at the start of the invasion rural populations were greeting the German soldiers as liberators! Only the terrible violence and disrespect of human life of the German invading forces changed all this.
In many countries (except for Denmark, perhaps) the German forces were loathed by the population because their violence, looting and, in particular, the terrible retaliations they extracted because of partisan actions (check the massacre of the Fosse Ardeatine in Rome).
Japanese forces incredibly used exactly the same (or even worse) methods in China. You can have a look at the Nanking massacre to have an idea. Again the Japanese forces considered the Chinese not worth of human status so they treated them with extreme and horrible violence.
The Koreans also were treated by the Japanese as human workhorses to be used and disposed of accordingly.

You can consider a lot of examples and cases that will point you to the conclusion that both nationality treated badly the populations they conquered (indiscriminate killing of civilians, looting, violence, starvation, etc.); the staggering number of deaths in Russia and China alone testifies to this.