If said device uses un-encrypted connections (straight http, not https, or FTP), then you can either capture data stream on your routerboard, move log file to PC and analyze it using wireshark, or you can mirror port, connected to said device, to another port and use wireshark live on that mirrored port. If communication is not encrypted, then you will be able to see what kind of commands (http request, FTP get) device uses to transfer the data.