How would I connect multiple ground wires in this case (replacing ceiling pendant lights)?

Yes, those three loose ends would be connected. That creates continuity to all involved circuits and fixtures. You really can't goof up grounds if everything is linked in a proper manner.

• Green wire from the pendant
• Bare wire from the mounting bracket
• Bare wire from the supply cable

You will want to connect the green wire from your light cord to the green or bare wire from your ceiling electrical box to the bare copper wire from your light bracket. Use a yellow wire nut if in the USA.

Just to add to the other answer, you don't need to mess with the bare wire "loop" that connects the two parts of the fixture, but if it does come apart, make sure you connect the wire coming from the screw on the dish-shaped part on the right to the other ground wires to ensure all parts of the fixture are property grounded.

"Why do this at all?" -> If something shorts out inside the lamp, we don't want the metal parts of the lamp energized because that could kill a loved one.

"So that means we should make sure every part of the lamp is grounded, right?" -> Yup.

So let's ground stuff...

The hanger: That's easy; it has a ground wire coming directly off it.

The ceiling rose: It already has a factory-provided ground wire going to the hanger, so if we ground the hanger we should be all set.

Oh, but hold on. This is a pendant light. Past the ceiling rose, it's all a plastic cord. Plastic does not conduct electricity. What grounds the hanging part of the lamp?

The green wire inside the pendant cord does that. However that is not connected to the hanger or ceiling rose. So we must connect it separately to ground.

So yes, you collect up both the bare line from the hanger and the green line from the pendant cord, and take both of them to ground. If you're attaching to a facility that only takes one wire (e.g. ground screw on metal box) you'll need to pigtail the ground.