How is a J-Head Extruder Head attached to the Prusa i3 rework?
It looks like the hotend may not be all the way in, are you sure it's not stuck?

If it's stuck and you can get it in further, those holes should go directly through the smaller ring on top of the J-Head.  You just need to run a machine screw into each hole to secure the hotend. The screw will need to at least be flush with the other side to work correctly.