For purchases, you can find your customer's emails here: Customer Emails
If you have the "Email Capture" option enabled in exchange for a free download in the product's edit page, you can view your email list here: Free Download Emails
You can also find collected emails within your respective accounts on Mailchimp or Aweber if you have those marketing integrations connected.
IMPORTANT: When using the Free Download Emails link above, please ensure to use the drop-down filter and filter to "Downloads" to see these specific emails. Also, free downloads in exchange for social media follows will not capture emails.