This is one of the Wardstone Chronicle (AKA The Last Apprentice) books by Joseph Delaney. Without more detail, it's quite hard to pinpoint a specific book but The Spook's Battle (AKA Attack of the Fiend), for example, mentions a character named Alice, demon-hunting with a master, a staff with a hidden blade, etc.
The Spook was finally satisfied, and we moved on to something he'd
only introduced me to a few weeks earlier.He handed me his staff and
led me to the dead tree we used for target practice. I pressed the
lever to release the hidden blade in the staff and then spent the next
fifteen minutes or so treating the rotten trunk as if it were an enemy
threatening my life. Time and time again I drove the blade into it
until my arms grew heavy and tired. The most recent trick my master
had taught me was to hold the staff casually in my right hand before
quickly transferring it to my stronger left and stabbing it hard into
All of the books in this series bear the legend
NOT TO BE READ AFTER DARK
on their back covers.