You can easily create a segment to identify your contacts who have not confirmed opt-in yet. To get started, head to your Audience page, click "Segments", then "Create a new segment". You'll want to find contacts based on contact information, where the confirmed opt-in field is empty -- and for your reference, here's a screenshot of how you'll want to build your segment:
Once you click "Add" then "Save", you'll see the list of contacts who haven't confirmed opt-in yet. Also, you can export that segment while viewing the main Segments page, or after opening up your newly-built segment.
That should do the trick, but let me know if you have any follow-up questions for me, Lucia!