The shortcut is found under Format, Font, Character Spacing, Use None or
⌥⌘[ (Tighten) and
This is missing from the inspector window and there is currently no way to see if and how much tightening was applied to text. You would have to go back to the above Use None to reset to zero and then re-adjust the kerning. In keynote 09 you had sliders for Character Spacing and Line Spacing next to each other which made adjusting text in a fixed size Text Box a breeze. Hope this feature will come back with the next update. It is sorely missed.