For an outgoing call the CDR field 'to-dn' will show the virtual number of the trunk used (e.g. 10002), so make sure this field is actually being output.
To link this virtual number to the real name of the trunk you need to go to SIP Trunks: As you start typing the virtual number in the search box so the SIP trunks displayed that match the whole or part of the input string will update.