From FreeCAD Documentation
- Select one or more sketch elements that support internal geometry (ellipse, arc of ellipse, arc of hyperbola, arc of parabola or B-spline).
- There are several ways to invoke the tool:
- Press the Show/hide internal geometry button.
- Select the Sketch → Sketcher tools → Show/hide internal geometry option from the menu.
- Use the keyboard shortcut: Z then I.
- Internal geometry is deleted for selected elements with a complete set of internal geometry, else missing internal geometry is recreated.