To view the subscribers who haven't confirmed their subscription, follow these steps:
1. Click on the list name
2. Click on subscriber actions
3. Click on Browse subscribers
4. Click on the blue bar that says: Click here for search filtering options.
5. Click on add new rule --> Subscription status
6. Select Is --> Opt-In Pending.
7. Click on Apply Filter button.
You will now see all your non-confirmed subscribers for that list.