Is there any place in the SE-universe to ask a question or seek for help in identifying an old (probably pre world war II) postcard, based on its front image (reproduction of Carl von. Bergen XIX century painting in this case) and printed information on the back? I am particularly interested in identifying the age of this post card or a year when it was published.
Or would such a question be off-topic everywhere (since identify-this-like questions aren't really liked anywhere)?
Depending on the specific framing of your question it may be on-topic on either History Stack Exchange under the identification and germany tags, or on Genealogy & Family History Stack Exchange under the germany tag (Carl von Bergen was a German painter).
If you decide go for the latter, do carefully read through What is “Genealogy,” “Family History,” and “Microhistory”? first. There was recently a question asking for translation of a WW1 German postcard which belonged to the OP's great great grandfather and it received a fairly detailed answer.
General "identify the place or thing on this postcard" questions are likely also on-topic under the [identify-this] tag at Travel.SE. Successful questions in that tag tend to be ones that are identifiable (major and minor landmarks count, random cafes and fire hydrants not so much) and interesting from a travel perspective. Since postcards generally fulfill both criteria (they tend to represent notable landmarks or vistas, and are generally recognizable to locals and frequent visitors), they are a good match for the site.
You specifically stated that the postcard has a print of a painting on it. A Travel.SE question could inquire as to where one might go today to view the original paining, and the site might also be open to identifying a postmark or stamp with a geographical location.
