“Why have I survived the war? Why was I the last person in my immediate family to be alive”? (p. 179). What does Ishmael learn by asking these “Job”-like questions?

By "Job" are you referring to the Biblical "Job"? I think Beah is an example of innocent suffering. Any child in war is an innocent. Beah is looking for reasons to his suffering. Unfortunately there are no good ones. The causes for strife and civil war in barely functioning countries like Sierra Leone are complex. Greed and power extend beyond the country itself to foreign interests that drive much of the strife. Like Job, Beah wonders what he has done to deserve such a fate.