"define its transform position of a bone that in on a model"? I have no idea what that is supposed to mean. Please consider rephrasing.

Your description is quite poor. Do you mean the OnMouseUp function which only happens when the mouse is released over an object with a Collider or OnMouseUp in general which would be if(Input.GetMouseUp(0)) or the like?

Going from what you describe in the latter part of your question, you want an object "laser" to move with some other object "bone", right? That can be achieved through parenting:

var bone : Transform; //instance in the scene. Get it however you like.
var laser : Transform; //prefab
var offset : vector3; //Where to place laser relative to bone

function OnMouseUp() (
    if(!laser || !bone) return;
    var instance : transform = Instantiate(laser, bone.TransformPoint(offset),
                                           bone.rotation);
    instance.parent = bone;
)

If your laser is a particle system or something that you turn on/off often enough, it is simpler to just add this part to the prefab and turn it off/stop emitting. Please see the 3D platformer tutorial's jetpack example of how to do this.