If one worked in ISP side and the subscribers complained about Web Page latency, and I need to monitor and catch the packets to resolve the issue, which software or way to do that?
Many Thanks for all
Without any specific information about the ISP side I can only recommend you use Wireshark directly on a subscriber's computer. You will get all packets from them and all packets that make it to them.
If you want something more specific then you'll need to provide more details about the hardware and topology of the ISP.