declare @T table(XMLCol xml)
insert into @T values
('<Root xmlns="http://tempuri.org" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">
<Elem1 type="T1">
<DisplayName type="string" display="Display name">No this</DisplayName>
<Name type="string" display="First name">John</Name>
<TimeZone display="Time zone">
<children>
<DisplayName type="string" display="Display name">GMT Standard Time</DisplayName>
<HiddenName type="string" display="Hidden name">GMT</HiddenName>
</children>
</TimeZone>
</Elem1>
</Root>')
declare @Node1 varchar(50)
set @Node1 = 'TimeZone'
declare @Node2 varchar(50)
set @Node2 = 'DisplayName'
select N2.Value.value('.', 'varchar(100)') as Value
from @T as T
cross apply (select T.XMLCol.query('//*[local-name()=sql:variable("@Node1")]')) as N1(Value)
cross apply (select N1.Value.query('//*[local-name()=sql:variable("@Node2")]')) as N2(Value)