Q: Where are Contacts stored in El Capitan?

If you use iCloud, then once you sign into iCloud from System Preferences and enable Contacts they should sync to your Mac.

Do you synchronize your contacts with a network service such as iCloud? If so, all you have to do is recreate the account settings.

This folder needs to be restored:

~/Library/Application Support/AddressBook

Please open the Library folder in your home folder by holding down the option key and selecting

          Go ▹ Library

from the Finder menu bar. Navigate in the usual way to the item indicated.