Just that. Type in /inspect [PLAYERNAME] and the inspect screen will appear. You should also be able to click on someone's name on the social tab and have an inspect option available.
Doesn't matter if they have to be in the same location as you to be inspected with the command or not, as long as the command exists.
(Yes, maybe it might not make much sense, but does it really make much sense for thousands of players to kill Lord Vanaduke hundreds of times when he really only lives once? To go back to the burning palace with Vana waiting to fight you when you already unlocked a mission where the palace has plants growing in and Vana is gone for a long time? Many things in this game don't make sense like that, so why not add this, even if it doesn't make sense?)
I think the command is great but it only does work on knights in the same area as you as the game has loaded them and their assets into the same area as yourself, thus it can access them. Without having a player loaded in it'll prevent that.
So I think it's more a technical limitation rather than a "it makes sense!" limitation.
I do agree that an /inspect command would be nice. Inspect when they're not loaded in nah. It would be nice if the player was already loaded in that your game would remember what they had equipped and you could inspect what you saw on them last, but if that data isn't stored (or causes too many problems to store) then it's unneeded.