Facing the wall section that needs to be removed, the bookcase is directly to the left, on that wall (not the one in the corner, but the next one over (x:484 y:115).
You need to mouse over the specific book, on the middle shelf. There are 3 or 4 books on the far right side of the middle shelf; immediately to the left of that is a single book that is sticking out, tipped forward, which is the one you need to click on (essentially, the one not highlighted if you mouse over anywhere else on the bookcase).
