Where are Denon products made? Japan? China? Somewhere else?

Varies by unit, e.g. 3805 Japan, 1604 China.

How can I find out for each unit?

Craig, look at a picture(e.g. Crutchfield)of the back panels. Dividing line appears to be 2805 Japan/1804 China, 2900 Japan/2200 China.

Thanks.