In a part?... thet's where the three primary planes intersect (xy-, yz-, zx-planes)
in a product? the first part's origin is the assembly origin. if you fix a part (set a fix-constraint) you can edit the fix constraint to see the position relative the assy-zero
I add "Translation or Rotation" command to my "Move" toolbar in assembly
While in Assembly Design click on the command and then the part or product, then click on the "Position" tab for location.