I have a /ping command that shows ping in chat, nothing fancy like a GUI, but it could work until someone else does a GUI
Players can "/ping self" to see their own ping, or "/ping <player>" to see another player's ping
Super Admins can "/ping" to list all players' ping for all players to see.
I made it a few years ago, and now that I look back at it, I would have coded it differently now, but it works just fine.
Give me a few minutes and I'll find it, take it from the bunch of add-ons that I have it packaged with, repackage it, and upload it.EDIT :
Download