WoW:API UnitLevel

Retrieves the unit's level. unit being target,party,pet etc.

EX:

 /script SendChatMessage("Level "..UnitLevel("target"));

will say, if you're targeting a lvl50: Level 50

As of some patch (1.5?) it will return -1 if the level is unknown (ie, you're too low to know it, or it's a special boss)
--- tarp (first post, probably broke all the design rules :) )

Details

Note that the value returned by UnitLevel("player") will most likely be incorrect when called in a PLAYER_LEVEL_UP event handler, or shortly after leveling in general. See PLAYER_LEVEL_UP arg1 for the correct level.

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