They're unprintable, so you can't see them by definition. You could replace them with some form of representation. For example,

sub unchomp { $_ = $_.$/ foreach @_ ? @_ : $_; }

while (<$sock>) {
   chomp;  # Don't want to transform the newline.
   s/([^[:print:]])/sprintf("\\x{%02X}", ord($1))/eg;
   unchomp;
   print;
}
[download]

Update: Tested. Fixed bugs.

Update: Here's an alternative representation (for charsets based on ASCII):

sub unchomp { $_ = $_.$/ foreach @_ ? @_ : $_; }

while (<$sock>) {
   chomp;  # Don't want to transform the newline.
   s/([\x01-\x1F])/'^' . chr(ord('@')+ord($1))/
   s/([^[:print:]])/sprintf("\\x{%02X}", ord($1))/eg;
   unchomp;
   print;
}
[download]

The first program outputs
test\x{1}\x{2}\x{1D}test
and the second outputs
test^A^B^]test
for the result of the Perl expression
"test".chr(1).chr(2).chr(29)."test"