Hm I would say it could be something with the collision, check on what element did you add “OnTouch” event , maybe you added it on something else than your Book Mesh, then check your static mesh what kind of collision it has and remake it if you need to, usually is best to just make a simple box collision.
Other way would be to import a simple box static mesh and make it invisible, and use that as touch-trigger event.
Also note that “touch” is meant to be used on touchable devices, while for windows you’d obviously use On Click.