The fuse for the rear trunk light is *almost certainly* found in either the main under-hood fuse box or the smaller interior one if it exists. It's *unlikely* to have a separate fuse panel just for the trunk light.
To be certain, consult your owner's manual. It will have diagrams showing the fuse panel layout and what each fuse controls. If you don't have the manual, you can usually find a digital version online through a Cadillac parts website or a site specializing in car manuals.