You mean how many object in one spread ? Cause you can't select many objects in different pages/spread.
In this case, one solution is to select your objects, go to Edit>import and links (may be its not the right appelation, I've a french version of CS6)
You would have a new panel opened with your selection imported and the number of object on the left top corner.
I don't see anything else.
Hope it's help.