If you're looking for a very specific data flow, this might be do-able on a Cisco device alone. You can get basic packet source / destination information like this.
ip access-list extended acl-track-flow
permit ip host 10.2.3.4 any log-input
permit ip any any
log-input will cause the router to generate a syslog message every time the ACL entry is triggered, including the MAC address of the packet.
For more detail, you could use "debug ip packet acl [detail]", which should be run with an ACL filter to keep it from cratering your router.
Finally, you can do "debug ip packet acl dump", which is a hidden command. This will actually show you the full contents of the packets that match . Seriously un-recommend running this on a production router without a very specific ACL for a very small flow.
The correct answer is to configure a SPAN port on the downstream switch that mirrors all traffic on the router port to a Wireshark (or similar) capture device.