... find position [i.e., index] specific word like "DATA LIST" in an array , but ... it can have spaces before or after ... [emphasis added]

Another approach. Searches for the words separated by one or more of any whitespace character; this could easily be refined to a single space. Be sure you understand   List::MoreUtils::indexes and regexes before you turn in your homework.

>perl -wMstrict -le
"use List::MoreUtils qw(indexes);
 ;;
 my @ra = (
   'DATA', 'LIST', 'DATALIST', 'FOO', ' DATALIST ', 'data list',
   'DATA LIST', '  DATA   LIST  '
   );
 ;;
 my $search = qr{ DATA \s+ LIST }xms;
 ;;
 my @indices = indexes { $_ =~ $search } @ra;
 print qq{at index $_ found '$ra[$_]'} for @indices;
"
at index 6 found 'DATA LIST'
at index 7 found '  DATA   LIST  '
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