@spaceboy
You can do that on pfSense directly with Diagnostic > Packet Capture.
Select the interface the client is connected to and enter its IP and start the capture. Access the remote site, then stop the capture to see the result. You will find all IPs the client had called.
However, it would be more reliable to know the host names, because a host name can be resolved to multiple IP, while the client only call one of it on a single access.
Since I don't know what your client really tries to access, I'm in the dark here.