I don't see in the documentation for Tk::LineNumberText anything about the method index() being available the way it is for Tk::Text.

Having said that, though, it appears (to address your second question first) that you could access the subwidget like this:

use strict;
use warnings;
use Tk;
use Tk::LineNumberText;

my $mw = MainWindow->new;
my $t  = $mw->LineNumberText('Text')->pack();

$t->insert('end', "This is some\n");
$t->insert('end', "normal text\n");

$t->bind('<Button-1>'  => [\&updateStatus]);
$mw->bind('<question>' => [\&updateStatus]);

# Debug section -- shows objects' keys
use Data::Dumper;
my @tkeys  = keys %$t;
my $sw     = $t->{'SubWidget'};
my @swkeys = keys %$sw;
printf "LineNumberText keys .... %s\n", Dumper([@tkeys]);
printf "Subwidget keys ......... %s\n", Dumper([@swkeys]);

MainLoop();
    
sub updateStatus {
    my $text   = $sw->{'text'};    # Get Text obj (Not really a good p
+ractice!)
    my $status = $text->index('current');
    print "$status\n";
}
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Note, however, that the line my $text = $sw->{'text'}; breaks the OO encapsulation; you're not really supposed to be accessing the data from the Tk::LineNumberText object directly (and the interface could change in the future, leaving you out of luck!)

Maybe you could suggest to the author of Tk::LineNumberText to put in a method to access the underlying Text object.

For your first question, I'm not exactly sure what you're asking.  The line $mw->bind('<question>' => [\&updateStatus]); shows how you could bind the question mark "?" to the subroutine, but it sounds like you're asking more about the cursor keys in particular.  Can you be a bit more specific about what you're trying to do?