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...

public void init() {
  super.init();

  // this is the reference to JQuery
  getAjaxSettingsgetJavaScriptLibrarySettings().setBackingLibraryReference(new JavaScriptResourceReference(....))DojoReference.class);
  
  // wicket-event.js
  getAjaxSettingsgetJavaScriptLibrarySettings().setWicketEventReference(new JavaScriptResourceReference(....));

  // wicket-ajax.jsDojoWicketEventReference.class);
  
  getAjaxSettingsgetJavaScriptLibrarySettings().setWicketAjaxReference(new JavaScriptResourceReference(....))DojoWicketAjaxReference.class);

}

Since Wicket 6.0 ResourceReference can have dependencies and it is recommended to properly define the dependency chain between this classes.
See the code of org.apache.wicket.ajax.WicketAjaxJQueryResourceReference to see how the default JQuery based implementation does that.

If the user application needs to This way the user application can upgrade/downgrade to new/old version of JQuery or even use YUI as backing library with the respective implementations of wicket-ajax and wicket-event based on YUI.then just the first line above is needed:

  getJavaScriptLibrarySettings().setBackingLibraryReference(AnotherVersionOfJQueryReference.class);