Ahhh ! Tricky tricky question !
All of the books are just sitting there, "RESTING" on the table. They're not slipping, sliding, rising, falling, rolling, swinging, swooshing, wandering, strolling, or meandering. Just "RESTING" in their stack.
None of the books has a changing speed or direction of motion. So none of the books is experiencing any acceleration.
So the NET FORCE on any book must be zero.
Pick a book. It doesn't matter whether you picked the bottom, middle, or top book. And the book's mass, weight, color, age, author, cost, or topic also don't make any difference. If the book is not accelerating, then the NET FORCE on it is zero. Just ask Dr. Newton. He'll tell you "F = m A" .