It is rare these days that I use a DS command, but in this case it worked out well. Use the command below do return the attributes that are currently stored on in the Global Catalog in your domain. This command was executed with administrative level permissions on a Domain Controller. Replace YourDomain with the correct LDAP information.
dsquery * "cn=Schema,cn=Configuration,dc=YourDomain,dc=com" -filter "(&(objectCategory=AttributeSchema)(IsMemberOfPartialAttributeSet=TRUE))" -attr LDAPDisplayName -limit 0
The resulting list are the attributes in Active Directory that are also in the Global Catalog.