You have custom attributes set up. You don't see the desired attributes in the merge field lists within an acknowledgement email, notification email or eReceipt. You want to add these attributes as merge fields to the acknowledgement email, notification email, or eReceipt.
At this time, the Acknowledgement email and eReceipts do not allow for additional merge fields to be added, other than what is listed. It's not possible to add a custom attribute to be a merge field in these areas.
After the information is downloaded into The Raiser's Edge, you may create an export and then email the information to the participants, using a custom merge fields in a CSV file as an Imported List.