one question you have to ask yourself is how YOU would find it, you as a totally blinded person. if you dont know the class and dont want to use a reference, its basicaly impossible to tell the game to find it.
now, what specifically you want to find? an actor can be a cube on the floor, a bird, a boss a player, an npc. if you want to find a player and its multiplayer, Gamestate has an array of player, each one has a playerId (which you can have on login). anything else im not sure…you would have to tag them, do a Get All actors of class and compare the tag.