If you duplicate an object in edit mode with Shift+D, and then hit P to make it its own object, it deselects and remains in place over/with the original object. What’s the keyboard move to determine/select the duplicate object from the original one (not using the outline)? Andrew Price does this too fast to figure out.
If multiple objects are very close together or even overlapping entirely and visually indistinguishable from one another, you can use Alt + right click to get a drop-down menu that allows you to choose from a list of objects in that area.
In the screen shot below there are actually two identical cubes overlapping. The menu lets us choose which one to select.