What is 3D viewpoint and what setting should it be?

Nope. Sounds unique to the LG. If you fiddle with the setting, let us know what it changes.

You mean pop-out? Like it popped out of the monitor?

Sounds just like what happens when I adjust "Horizontal Shift" in a 3D video editing program. If so, that would be shifting how far apart the two eyes' view of the scene is, which has the effect of moving the screen plane forward or back, making objects appear to pop out or recede into the TV.

(Of course you cannot change what the stereo cameras captured when they were filming. All you adjust is how far apart those two images are projected when you view them back on the TV screen.)

That might be useful at times, especially on a TV screen that is significantly smaller than the movie screen a video was originally made for. Increasing the setting will tend to make things look a little more 3D, at least until an image pops out too far. It doesn't look right if an object popping out of the screen touches the screen edge, so we adjust the horizontal shift to where that doesn't happen much. On a large screen, we would probably want the setting at 0 to match what the movie director intended, because they have already adjusted the horizontal shift scene by scene and moment to moment.

I was wondering about this. My 3D blu ray player (panasonic) has the option from -5 to +3 but I can't really notice the difference when I adjust it end to end.

So positive is more 3D-ish and negative flattens it out? Or the other way?

It adjusts between depth and convergence.

Best to keep it as close as possible to 0. On my Samsung, it was a firmware upgrade that helped fix the crosstalk problem.