The camera position is in XYZ coordinates. There isn't a quick and simple way to find the XYZ coordinates of a particular lat-long coordinate in Terragen. You'd need to use some maths. However, I'm guessing from your question that maybe you've brought in some geo-referenced terrain and it's nowhere in sight, and that you just want to bring it into view. In that case, there's a way to set up your scene in Terragen so that a particular lat-long is centred at the 0,0,0 coordinates (the origin) in the Terragen world. so that any terrain appearing at that lat-long will be centred around 0,0,0 in XYZ. To do this, copy the lat-long coordinates you're interested in and enter (or paste) them into the Planet object's Lat-long at apex parameter. Now, as long as the camera is not too far from the origin, which shouldn't be a problem if you're working with the default scene, you should be able to see the terrain.
Matt