Hello
I don't think you can add custom attributes to Glossary Term today
One walk around you can try is to define a new Glossary Category like "Data Owners"
Then you can define the list of data owners as terms under that category
Next you can choose another Glossary Term, choose "Related Terms", you can choose one relation type, e.g. "isA" and link to the data owner Term you defined earlier
Hope this helps