Print variable views template
This is the path for accessing single fields in a view table template, for example in the first row:

rows.0.columns.fieldname.content.0.field_output


In your code example, to get all field names available, use this in the first loop:

{{ dump(row.columns|keys) }}


The naming of the fields depends on how you have configured the view and is not necessarily the machine name of the field in the entity.