finding vertex numbers in Irrlicht add-on ?

[Burgs]

Greetings,

  I have recently begun experimenting with the Irrlicht (Au3Irrlicht) component.  One of the example scripts included with it demonstrates how to attach a 3D model to another (the example places an object in a characters 'hand').  This is accomplished using a particular vertex # in the model as the attachment point.  My question is that I'd like to know how one is to go about knowing what the number is of the desired vertex?  For example as just mentioned how is the proper vertex number in the character's model (hand) determined?  How was that particular vertex number (don't remember the actual # used) known to be part of the model's hand and suitable as the attachment point?  The documentation included with the Irrlicht add-on is a bit sparse and doesn't seem to mention it.  Thanks in advance for any help.   Regards.