Question

If the 'S' after Rubbel is not necessay - why? To my understanding a genitive governed noun needs an 's'. Is this because Rubbel is a name?

Answer 1

The first option is correct. The S would be correct if you would use the phrase "Alfred Rubbels Kriegstagebuch". I think it has something to do with Rubbel being a name because if this would be the diary of a stone you´d say "Kriegstagebuch des Steines.

Answer 2

No. It is "Kriegstagebuch" because it is a combination of "Krieg" + "Tagebuch" so there is an s between the two words. "Tagebuch" is a fixed term just meaning diary and regarded as one word only (I'm a German).