Where to find Epic Clone?
When you clone a work item in Jira Cloud using Epic Clone, a dialog will pop up allowing you to configure the cloned item and its children. This guide highlights the location of Epic Clone within a Jira work item. Let's consider cloning this Epic using Epic Clone:

It includes several child items as stories or tasks and some of them have sub-tasks.

By clicking on the three dots → Clone Work Tree, you can open the clone configuration dialog.

Please proceed on this page where it is explained what you can do when cloning a work item with Epic Clone.