my $largest = @table ? $table[0][0] : undef;
for my $y (0..$#table) {
   my $row = $table[$y];
   for my $x (0..$#$row) {
      $largest = $row->[$x] if $largest < $row->[$x];
   }
}
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Same idea for more dimensions. If the number of dimensions is variable, you can use Algorithm::Loops's NestedLoop.

Update: Fixed bug in code.

For 2d:

use List::Util qw[ max maxstr ];

my @data2d = ...;

my $max = max( map max( @$_, ), @data2d );
[download]

Or for multi-dimensional:

use List::Util qw[ max ];;

sub maxNd { max( map{ ref() ? maxNd( @$_ ) : $_  } @_ ) };;

my @b = ...;;

print maxNd( @b );;
9981
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If you have an array @a, using it in a scalar context gets the number of elements:

my @a = ( 3, 1, 4, 1, 5 );
my $N = @a;
say $N; # or print "$N\n; before 5.10
my $aref = \@a;
$refsize = @$aref; # or @{$aref};
say $refsize;
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For a multidimensional array, you wind up with a reference to the inner array, so use the ref example:

my @twoD = ( [ 1, 2, 3 ],
             [ 4, 5, 6 ],
           );
print "Top level or array has " . scalar @twoD . " elements\n";
for my $row ( @twoD ) {
   print "row has " . scalar @$row . " elements\n";
}
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perl -le 'my $max="-inf";$array=[[100,20,[32,4]],51,[621,7],[82]];
sub fm { map { $max = ($max < $_) ? $_ : $max } 
map { ref() ? fm($_) : $_ } @{$_[0]} };
fm($array);
print $max '

621
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Your program has a bug. Had you enabled warnings, you would have found out why. You never initialize $max, which means that in numeric context, $max is treated as if 0. Which means that if all your values are negative, at the end of the procedure, $max is never assigned a new value and still undefined.

You ought to initialize max to negative infinity:

my $max = "-inf";
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- - for removing the original question and replacing it with a 'thank you' note.

One can hope the consideration process ( will have | quickly ) led to restoration of the original, but since we're here...

Removing original content (in the manner in this thread) leaves replies less useful than they may have been prior to the editing of the OP: it leaves the replies without context.
Emending content without explanatory notes of just what was changed creates a context different from that a reply was intended to address. That's misleading, at best.

In short, don't modify your posts without notice. ( <strike>ing is just one mode of providing notice without changing context. )