To list the external references:
- In the FeatureManager design tree, right-click the feature, component, body, or part and select List External Refs.
- View information and set options in the External References For dialog box as described below.
- Click OK.
Also check these links:
Since it is a sketch, you can open the sketch, pick Display/Delete Relations and then pick External under the down arrow. If you are very lucky, you can Delete All and move your sketch.