Suggested answer:
(1) The following is an example where English blank does not mean the same as Norwegian blank:
The Vizefeldwebel watched the exchange with a blank face...
English blank and Norwegian blank are considered to be false friends because they are similar-looking and similar-sounding words in two different languages, but they differ in meaning. In the example cited from the corpus, blank has the meaning "expressionless" and does not correspond to the meaning of Norwegian blank in similar collocations, i.e. "shiny".
(2) Yes, the word blank can have the same meaning in the two languages, as shown in the follwing example from the corpus:
... we are to explore the visual possibilities of making marks on a blank sheet of paper.
The Norwegian expression "en blank side" comes close in meaning to the English example.
(3) There are seven occurrences of the collocation blank wall in the corpus:
Praying men stand in dense lines facing a blank wall in the direction of Mecca..
In this example blank is a false friend of Norwegian blank; if you use the expression "blank vegg" blank does not suggest an empty wall, but rather a shiny wall.
Read about false friends here.
Terminology: false friends, collocation.