This does depend on the version that you have, you can add the External document No. if you have the full version of Warehouse Insights.
For the Express version out of the box it is not possible to add additional columns.
On the full version, if you navigate to the Warehouse Insights Applications < The column Tab.
Add the Event ID and Table No. it the field exists on the table; you can drill down to the field name and add it.
However, if the field does not exist on the table, instead to drilling don add -1 as the field No.
Next check the is formula Boolean, then add an Override value, this value is a formula, hence the check for ‘is formula’. You need to know the Table and the field no, a formula can look something like this
The first number is table No, next is the field no, then you have the where the data is coming from that you are adding to the line.
37,10,WHERE (Document No.=FILTER(‘[Source No.]’))