$handle is an output parameter; it is just a integer pointing to a block of memory that Devel::Leak::NoteSV is using to store its internal table. The documentation should probably read:

  use Devel::Leak;
  ... setup code

  my $handle;
  my $count = Devel::Leak::NoteSV($handle);

  ... code that may leak

  Devel::Leak::CheckSV($handle);
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Also, be aware that most production builds of Perl do not have -DDEBUGGING turned on, and that the Devel::Leak documentation says:

Note that you need a perl built with -DDEBUGGING for sv_dump() to print anything, but counts are valid in any perl.

So, if you were expecting Devel::Leak::CheckSV to give you the details of the leaking objects (as I was when I played with it), you may be disappointed. You can use `perl -V | grep DEBUGGING` to check your build.