I have a quick solution for your first question: additional email addresses will show as a separate column if you export all of your contacts via the "Actions" button in your contact overview and select the option "Include all email addresses".
The secodary email addresses will be listed in the column "Additional email addresses" in your export file.
Regarding your second question - I checked our documentation and I believe it's currently not possible to bulk delete secondary email addresses in HubSpot.
You could delete the email addresses manually by importing a list of contacts that have more than one email address and working through them one by one.
I know this is not ideal if you're working with a large number of contacts, that's why I wanted to ask a couple of API experts if they can think of a workaround:
hi @Gonzalo & @lynton, can you think of a way to bulk delete additional email addresses with the help of an API? Thank you!