To find someone who has previously unsubscribed, you can search in your 'Contacts' dashboard
In the instance above, I'm searching all contacts, but if you wanted to search in a Group, the only thing step you need to do from this view is click into the Group from the left side.
To find someone who has unsubscribed, you will want to search for the email address
You may then see this screen.
Not to worry, that's because we're searching with the 'Status' Subscribers rather than Unsubscribes.
You'll now find your contact.
Top tip - even if you were to remove this contact from your Database, they can't be readded because NewZapp will recognise that they have previously unsubscribed.
If you then want to see when they have unsubscribed, you can click into this contact to open their Card:
Make sure to open the GDPR screen by clicking the tab and then you'll have the date and time that the individual has unsubscribed, or in this case been unsubscribed by an admin in NewZapp.