I run into this quite often where the client isn't sure which port the client is connected to.
In many cases, I do not have access to their network management system, or the network is down or worse, the documentation is dated and inaccurate. I think every network analyst should know how to do basic tasks like this one.
in some scenarios, I use Wireshark and capture a CDP packet to which switch, port, vlan, etc... or if I have a tool like a NetAlly Linkrunner.
In this example, I show you how to do it on a Cisco 2940, but you will find that this works on most models.