For those looking to respec on the Imperial side, go to co-ordinates (X,Y) 4770, 4520 on the main imperial fleet where all vendors are. For those looking to respec on the Republic side, go to co-ordinates (X,Y) 4640, 4880 on the main imperial fleet where all vendors are. There are several other places in the game to respec, but these are the two most commonly used since everyone has access to the fleet. You can view your current co-ordinates by pressing M and looking at the top left side of your map screen.