Here is what i would do
1) open the datebook input file.
2) open 'raise' file for writing in append mode
3) Iterate through the input file.
4) split each line based on ':'. As i understood from the above example is that name, phone number, address, date and salary is seperated by ':'.
5) build a hash making name as key.
6) calculate 10% increment and add it to the salary.
7) print the values to the 'raise' file.
8) close both the file handles.
9) iterate through the hash for printing the names appeared more than once in input file.

You can refer the following untested code for more information.

#!/usr/bin/perl 

use strict;
use warnings;
use Data::Dumper;

my %seen   = ();
open(FH,">>raise.txt");
while(<DATA>) {
    my ($name, $phoneno, $address, $date, $salary) = split(/:/);
    next if $seen{$name}++;
    #$seen{$name}++;        
    $salary += ($salary*10)/100;
    print FH "$name:$phoneno:$address:$date:$salary\n";
}
close(FH);

map {
    print "$_ appread $seen{$_} times in the file\n" if($seen{$_} > 1)
+;
}keys(%seen);

__END__
Barbara Kerz:385-573-8326:832 Ponce Drive, Gary, IN 83756:12/15/46:268
+500
Barbara Kerz:385-573-8326:832 Ponce Drive, Gary, IN 83756:12/15/46:268
+500
Barbara Kerz:385-573-8326:832 Ponce Drive, Gary, IN 83756:12/15/46:268
+500
Norma Corder:397-857-2735:74 Pine Street, Dearborn, MI 23874:3/28/45:2
+45700
Norma Corder:397-857-2735:74 Pine Street, Dearborn, MI 23874:3/28/45:2
+45700
Tommy Savage:408-724-0140:1222 Oxbow Court, Sunnyvale,CA 94087:5/19/66
+:34200
Tommy Savage:408-724-0140:1222 Oxbow Court, Sunnyvale,CA 94087:5/19/66
+:34200
Lesle Kerstin:408-456-1234:4 Harvard Square, Boston, MA 02133:4/22/62:
+52600
JonDeLoach:408-253-3122:123 Park St., San Jose, CA 94086:7/25/53:85100
[download]

console output

Barbara Kerz appread 4 times in input file
JonDeLoach appread 2 times in input file
Norma Corder appread 3 times in input file
Lesle Kerstin appread 2 times in input file
Tommy Savage appread 3 times in input file
[download]

raise file output

Barbara Kerz:385-573-8326:832 Ponce Drive, Gary, IN 83756:12/15/46:295
+350
Norma Corder:397-857-2735:74 Pine Street, Dearborn, MI 23874:3/28/45:2
+70270
Tommy Savage:408-724-0140:1222 Oxbow Court, Sunnyvale,CA 94087:5/19/66
+:37620
Lesle Kerstin:408-456-1234:4 Harvard Square, Boston, MA 02133:4/22/62:
+57860
JonDeLoach:408-253-3122:123 Park St., San Jose, CA 94086:7/25/53:93610
[download]

Update: commented out one of the hash increments as mentioned by GrandFather