I’m running Media composer 2.6.2, but I believe this to be a universal technique in the avid World.
2 different ways:
If your sequence is in the same bin as the clip,Highlight your sequence, go to the menu in the lower left corner of the bin, and select: SHOW MEDIA RELATIVES
The opposite technique is to go to your clip bin without highlighting anything, go to the same menu and: SELECT UNREFERENCED CLIPS. It will then highlight every clip not being used in any sequence living in any currently open bin.