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Trackback URL Tag
In order to display the trackback URL for an entry, so that people can send you Trackbacks, you must use the trackback URL tag:
{exp:trackback:url}
This is a single variable, so there is no pair of tags. Note that this is the URL that other people will use to submit a trackback for your entry. It is not the URL to the page you will use to display trackbacks for an entry.