In object mode , duplicate the curve at same location.
Convert duplicate to mesh. Enter mesh edit mode.
Select corresponding point.
Use Shift S menu to place 3D Cursor.
Go out of edit mode. Delete mesh. Go back to Curve edit mode. 3D Cursor should be at correct location.
2.Enable Extra Objects addon of Add Curve category.
At an arc object of correct angle and same radius of circle.
Enter Curve Edit mode, select extremity of arc. Shift S to place 3D Cursor.