You may be just fooled by an Illustrator interface weakness.
That is, if you see the Show Gradient annotator item in the View menu, it actually means that the annotator is hidden. Click the item to turn it on.
If you see the Hide Gradient annotator item, it means that it is turned on.
Perhaps it would be better to rename the items to something like Annotator is on and Annotator is off. Additionaly I'd place it as an option box straight on the Gradient palette.
I understand that a gradient annotator (bar) is supposed to be displayed on top of the object that I am working on so that I may edit on the object itself rather than from the tool bar?
perhaps even more clear is a "radio" button style (perhaps better with 'dot in circle' instead of x / _ )
x show _ hide : Gradient Annotator
_ show x hide : Gradient Annotator
LOL! I'll take a guess, the Op selected the object and filled it with a graadient and no gradient annotator! Not relizing they have to select the tool itseklf in order to see the annotator.
This derives me crazy all the time.
Clicking on the tool should fill the object with a gradient and bring the panel into focus and make it active. It seems silly to have to click on the panel activate the gradient fill and then select the gradient annotator to manipulate it.
Just had the same problem, I was using the gradient tool in a shape that had been created by expanding a live paint group. The gradient annotator wasn't showing in some shapes, while in others, it showed just fine. In my case, somehow the problematic shapes were contained within a group (consisting of only the shape itself, go figure), that wouldn't go to isolation mode if I double-clicked it. Used "ungroup" on them and things got back to normal. If this fail, try to create a graphic style out of the shapes where the Grad Annotator is showing, then apply this style on the problematic shapes, or try to find if there's something wrong showing on the Appearance panel.