Hi Dmitry,
In show available fields, you will get the list of BOL entities available. You can either click on "SHOW TECHNICAL DETAILS" and then see for the fields required or go to Context Node level of the View and see the fields which you need.
For Example, Sales ORDER ID is available in BTADMINH. The field name is //BTADMINH/STRUCT.OBJECT_ID..
You have to click on the arrow mark to see all the fields available under BTADMINH.
Regards,
Karthik