Does this help?
Code:
public plugin_init() {
register_event("CurWeapon", "event_CurWeapon", "be", "2=29")
}
public event_CurWeapon(id) {
new isShown = read_data(1)
if (isShown) {
// Code here for when knife is pulled out
} else {
// Code here for when knife is put away
}
return PLUGIN_CONTINUE
}