There is usually one attached to the back of the driver side cylinder head on a stud. The other end of the strap connects to the firewall where the black plastic cowl meets the metal.
There are three actually. The primary body ground is on the passenger strut tower. There's another (engine ground) that goes down and bolts to the passenger side engine mount on the bottom. (Difficult as hell to get to....). The third is as msvela448 shows above.
No, the larger cable shown is a 4 gauge I added that goes to an alternator mounting bolt that provides an additional ground reference for the alternator. The motor mount/starter ground is inside of the plastic casing shown that's continues downward and towards the front then down again underneath the vehicle and bolts up underneath. The ground is G106.
I added a DOB kit a couple of years ago and found that I needed an additional ground as my system was floating and producing voltage drops (meaning it appeared my alternator wasn't working when in reality the problem was) resulting resistance differences in materials and items I added/changed. I figure that the new intake manifold w/additional anodizing and insulation; different alternator mounting location; alternator powdercoating; etc. resulted in resistance differences so I had to add a couple of grounds to solve the problem.