This is awesome. I have no idea what the heck they are talking about, but all I know is two smart guys I idolise are talking about rocket designs and I am okay with that.
We used the Space Mission Engineering: The New SMAD by Wertz, Everett, and Puschell for my senior capstone project.
It's pretty comprehensive about all things involved about space missions.
You would specifically want to look into its chapter about launch vehicles since that is what SpaceX does (they're basically launch-to-orbit-as-a-service). Dragon is their payload capsule while the Falcon is the launch vehicle (the rocket).
How does one view the actual conversation between the two? All I see is one tweet from ELon to johns and a bunch of random people commenting on that tweet