In APhoto, some tools are in "fly outs". If the button has a small black triangle, right click on the button to see the "hidden" tools. (The Smudge Brush is with the Blur, Sharpen and Median Tools).
Possibly it it not in the Toolbar, but it should be available in the app. Go to the menu "View" and click on "Customise Tools" (at the bottom of the menu). A panel will open right of the toolbar. You should find the Smudge Tool in it. Just drag it into the toolbar and close the "Customise..."-panel. Then it should work. At least I hope so.
Normally it should be available in the little menu in the toolbar where also Blur, Sharpen and Median Brush tool are available.
