The answer is...in the desert
If the book uses words such as "I" then its first person
If it uses "he, she" its third
If it uses "you" its second.
The skull symbolizes the great and famous victory they had during the war. The poem used the phrase "great victory" and "famous victory" many times. Famous in the sense that even younger ones like Wilhelmine and Peterkin would know because the skulls they saw become the proof of their great victory and is the cause of their freedom.
I believe the answer is idiom, the phrase is not comparing anything so simile and metaphor is out of the question, also personification is giving a non living thing human characteristics.