If we do not have a subscription to data.com, where are the field mappings held that dictate the fields for our list uploads in Marketo? Also, is there a place to view all Marketo field options when uploading a list?
When you import lists, Marketo uses the column heading names in the CSV file to map to its fields. You can get a list of these names for all of your fields by exporting one lead record and chosing the "All columns" option. Alternately, you can specify the mapping each time you import a list in Step 2 (see below).