How can I find the position of my weapon?

I have a character with two weapons now. When I export the fbx file and put into unity. Here is a group to group the character , bones, and weapons up. Then I drag the group into hierarchy and put their animations in this model. So that it can run and jump. But I find that it only affect the group model position when the character is running. I just want to see the weapon position. It doesn't change anything in position X,Y,Z. But it is really moveing with the whole character. So how can I get the real weapon position now? I want to do the trail renderer on the weapon.