I wanted extra information of members so I created a new collection as no new field can be added to privatememberscollection. But I want to have some connection between these two. Would referencing help? also if i include owner id in both tables will it be same for one particular user in both the collections?
Yes have a look at using reference fields for this, however when you add a reference field to your second dataset and link it to the Wix Members app own collection, then you will only be able to reference the users email address.
If you look in the Wix Members app collection, you will see this in the email field about it - ‘This is the field used when content is referenced in another collection.’
You can not change the primary field either, so you will have to stick with the email if you want to do it this way.