To see what XDoclet tags templates available for completion select JBoss Tools > XDoclet > Code Assist > Templates .
By right clicking on any tree element you can add a new template, remove or rename it and also add a new tree.
Select, for example, Add and you'll be prompted by a list of available elements to add.
By double-clicking some element a new list will be shown: now for available methods.
Choose any element from the list, then select an attribute.
It will be added to the available templates.