I've pored over the pictures and still I can't figure it out.
I know the second stage separates from the first stage using positive force from pneumatic pushers.
I also know that the payload fairing (the wider bullet shape used to deliver satellites to space) has a mounting plate which allows for any type of payload adapter chosen by the customer.
But the space station cargo resupply missions don't use the payload fairing---they use the cargo Dragon. And the cargo Dragon attaches to the Falcon stage through the trunk. So what is that connection like, and more importantly, what type of separation system do they use?
I assumed pneumatic pushers would be it, but this doesn't seem right. For one, there are no protrusions for pusher cylinders as seen on the interstage. If they could do without those protrusions between the second stage and the trunk, they would have done without them on the interstage too, it seems.
I do see a few things on the trunk that suggest mounting points. There are six of them arranged hexagonally. Picture below. These could be collets for locking, but there is no trace of a pneumatic cylinder here or on the second stage.