XML Query Question

Does this get you what you want?

DECLARE @x XML = '
<SearchJobConfig>
  <QueryID>1072</QueryID>
  <QueryString>
    <SearchCriteria name="Search query" >
      <ExpressionSet logicalOperator="AND">
        <SimpleAttributeExpression displayName="Date" npmPropertyId="4" searchOperation="GREATER_EQUAL" dataType="string" caseSensitive="false">2019-06-01T04:00:00</SimpleAttributeExpression>
        <SimpleAttributeExpression displayName="Date" npmPropertyId="4" searchOperation="LESS_EQUAL" dataType="string" caseSensitive="false">2019-06-13T03:59:59</SimpleAttributeExpression>
        <SimpleAttributeExpression displayName="Class" npmPropertyId="1056" searchOperation="EQUALS" dataType="int32" caseSensitive="false">65</SimpleAttributeExpression>
      </ExpressionSet>
    </SearchCriteria>
  </QueryString>
</SearchJobConfig>
'

DECLARE @Job TABLE(xConfig XML)

INSERT @Job ( xConfig )
VALUES ( @x )

SELECT j.*
       , ca.c.value('text()[1]', 'VARCHAR(30)') AS date_val
FROM @Job AS j
CROSS APPLY j.xConfig.nodes('/SearchJobConfig/QueryString/SearchCriteria/ExpressionSet/SimpleAttributeExpression') AS ca(c)
WHERE ca.c.exist('@displayName[.= "Date"]') = 1;

To get everything on one line, just do this:

SELECT *
FROM 
(
    SELECT STUFF(
    (SELECT N' ' + ca.c.value('text()[1]', 'NVARCHAR(MAX)')
     FROM @Job AS j
     CROSS APPLY j.xConfig.nodes('/SearchJobConfig/QueryString/SearchCriteria/ExpressionSet/SimpleAttributeExpression') AS ca(c)
     WHERE ca.c.exist('@displayName[.= "Date"]') = 1
     FOR XML PATH(N''), TYPE ).value(N'.[1]', N'NVARCHAR(MAX)'), 1, 1, N'') 
) AS x(date_val);

If you want the date values in the same row but different columns you can shred using nodes() to get one row per ExpressionSet node and then use attributes displayName and searchOption in value() to get start and end date.

declare @x xml = '
<SearchJobConfig>
  <QueryID>1072</QueryID>
  <QueryString>
    <SearchCriteria name="Search query" >
      <ExpressionSet logicalOperator="AND">
        <SimpleAttributeExpression displayName="Date" npmPropertyId="4" searchOperation="GREATER_EQUAL" dataType="string" caseSensitive="false">2019-06-01T04:00:00</SimpleAttributeExpression>
        <SimpleAttributeExpression displayName="Date" npmPropertyId="4" searchOperation="LESS_EQUAL" dataType="string" caseSensitive="false">2019-06-13T03:59:59</SimpleAttributeExpression>
        <SimpleAttributeExpression displayName="Class" npmPropertyId="1056" searchOperation="EQUALS" dataType="int32" caseSensitive="false">65</SimpleAttributeExpression>
      </ExpressionSet>
    </SearchCriteria>
  </QueryString>
</SearchJobConfig>
';
declare @Job table(xConfig xml);
insert @Job (xConfig) values (@x);

select T.X.value('(SimpleAttributeExpression
                   [
                    @displayName = "Date" and 
                    @searchOperation = "GREATER_EQUAL"
                   ]/text())[1]', 'datetime') as date_val_start,
       T.X.value('(SimpleAttributeExpression
                   [
                    @displayName = "Date" and 
                    @searchOperation = "LESS_EQUAL"
                   ]/text())[1]', 'datetime') as date_val_end
from @Job as j
  cross apply j.xConfig.nodes('/SearchJobConfig/QueryString/
                                SearchCriteria/ExpressionSet') as T(X);

Result:

date_val_start            date_val_end
2019-06-01 04:00:00.000   2019-06-13 03:59:59.000

You say that you want to retrieve multiple values from the XML, but then instructing your XPath to return only the first (#1) of them:

/ SearchjobConfig / QueryString / SearchCriteria / ExpressionSet / SimpleAttributeExpression [ 1 ]
                                                                                             \___/
                                                                     Returns indexed item #1 _/

Lose this indexing clause and you'll get both values back, in the order they appear within the input XML.

Further reading: https://www.w3schools.com/xml/xpath_syntax.asp

As far as getting them into a single line ... it's [almost certainly] possibly, but is it really worth the effort for only two of them? YMMV.