This question was answered by Jan-Willem van Dronkelaar, @jwvdronkelaar on blender.chat.
- Select Armature, click Rest Position
- Go into Edit Mode for mesh of character
- Highlight the vertex
- Press Shift+S > Cursor to Selected
- Switch to Object Mode
- Shift+A to add an Empty, which should be at the 3D Cursor & Vertex position
- With the Empty active, Shift select the character mesh
- Switch back to Edit Mode
- Ctrl/Cmd+P to Make Vertex Parent
- Select Armature, click Pose Position and the Empty should follow the Vertex
- To get the motion trail, go into the Object Properties of the Empty, go to Motion Paths, click Calculate
- After edits, recalculate the Motion Path by clicking Update Paths.
(With Blender 3.0, if you are in the Armature’s Pose Mode, when you right click there’s an option to refresh motion paths.)
Thanks again to Jan-Willem for this solution!