the easiest way to setup the flashlight and access the script it contains would be like the following. first add the flashlight as a component of the character, next drag the flashlight from the my components section onto the event graph (this is now a reference to the flashlight), drag off the reference and search for your toggle lamp event.
the next easiest method is for the case of if you are spawning the flashlight during game-play. in this case you would have a button to spawn the flashlight say F, so you press F then have the spawn actor of class node, the return value of the spawn node is a reference to the flashlight that was spawned so you save that to a variable of type flashlight ( in your case Linterna object reference). then when you want to use the toggle lamp event you just need to get the variable that contains the needed reference, drag off and search for the event.