In the View tab of the Options... dialog, check Enable function block hotspots.
Check this option to enable the link from the function block (the rectangle representing a particular function) to the Function Blocks Used on index. If Enable function block hotspots is checked, clicking on a function block hotspot in the content pane will cause the index of all the uses of that function code on that document to be displayed in the index pane. If it is disabled, clicking on a function block will have no result.
Note: Function block hotspots were added in DBDOC 10.6. They have a specific right-click menu, and among other things, allow you to add all the inputs and outputs of the block to the Watch Window in a single step.