Tracking coins: what happens at an exchange

I'm looking into following money flows, and was wondering about tracking coins on the public ledgers.

P2P it's easy, follow the coin exit one wallet into another. However how do we track outflows to/from exchange.

From what I can gather, exchanges appear publicly like "black boxes". We have no idea what goes on inside them. Unless an exchange pays special attention, there's no (public) way to track movements within the exchange either.

Also, As it seems the majority of trades occur on CEXs, is there any way to see total trades of any coin as an totality across all exchanges and off exchange transactions?