Just randomly give it a target. It doesn't matter really. Try (0, 1, 0) for the target. Close your eyes and spin around so fast you land on the floor, then get up and open your eyes- there's your target.
Once your world content gets underway you can do more things such as spawning the camera while looking at a particular wall.
To be crafty, if you don't know what coordinates your object is you want to look at-, give your camera a random target, then run the game. Manually move the camera to look at the spot you desire. Then have it spit out the current target vector (System.out or something)- use this as your target vector the next time you run your game.
So basically:
Camera.setOrigin(new Vector3df(0, 0, 0), new Vector3df(0, 1, 0), new Vector3df(0, 1, 0));
Then look at the spot you want, record the xyz of the target vector and use that as the value you init setOrigin() with.