Hello fisichel Welcome to the forum.
I was wondering first off is what type of connector are you using? That might help to determine what they are referring to as earthing cones.
The earthing cone I believe is used for shielding/grounding of a cable. Also referred to as EMC.
These are made to connect to the braiding of the Cable to help ground.
I was doing some searching and the products that show up are Cable Glands. For example These Options are set up for EMC.
Here is what I believe they are referring to
Also this was taken from the Datasheet showing how it will look connected
I hope this will help you out.
If you have any questions Please let us know.