Hi bisana,
use the Alfresco Web Client and using search you can find the document/folder, since all nodes are kept into Alfresco repository.
When you find the object you need, click on node properties, and then you can use Manage space users(for spaces) or manage content users from the right menu and look at permissions set for the node.
As an alternative, if you know the node id, you can use Alfresco Administrator's Node Browser and after selecting the correct SpacesStore from the left menu, perform a query using that noderef as key.
When you find the node you will receive all information about aspect, properties, associations and permissions.
Hope this helps.
Regards,
Andrea