To see Customer Attributes in Target, you first have to upload a Customer Attributes file and choose attributes to share to Target. Once you do that, you should see those attributes show up in the "Visitor Profile" list of attributes when you create an audience.
Can you try that? Or if I'm misunderstanding could you add a screenshot of what you're looking at?
You need to get provisioned for customer attributes.
It doesn't appear within the Target interface but it is a core service that appears within the Marketing Cloud user interface. I would suggest you to reach out to your account manager or client care to know how to get them enabled.
You can also look at the below documentation and know more on Customer Attributes: