What is the term when a novel begins with a scene that belongs closer to the ending? Not a prologue, not foreboding, kind of a hook.

There are several ways to describe this usage. It is not
precisely a flashforward, which usually occurs within the
story, giving information or prior knowledge of an event that has happened before,
outside the order of the proper time frame. A flashforward works in exactly the opposite
manner of its companion, the flashback. Your example is
probably closer to that of a prolepsis, similar to a
flashforward but not restricted to its placement within a later part of the story. A
prolepsis, like the flashforward, anticipates a future event of some kind, providing an
answer outside of its normal time frame.