This has not been tested by ME, but a few of my guildies have confirmed that it is working (last night)
Basically, what you do is get both the "CowTip" and "DogTag" addons. Apply these and when you see the tooltip for the opposing faction, it will tell you what spec they are.
I'll be looking into this more when I get home tonight.
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Or, you just get the addon Examiner from [Only registered and activated users can see links. ] and target an enemy player and write /inspect, then you can see it.
I like this better, cus you only need to get one addon, that you actually may want to use anyways, since it store the people you have inspected so that you can look at it later or so, it shows the players stats etc.