It seems that you have forgotten to use <?php
and ?>
properly. Remember to open and close the php tag like the following:
<?php if ( is_singular( array( 'rivista', 'rivista-trimestrale' ) ) ) {?>
<script>
jQuery(function($){
$('.parallax-window').parallax({imageSrc: '<?php echo $ilgelo_options['ilgelo-parallax-image']['url'];?>'});
});
</script><?php
} else { ?>
<script>
jQuery(function($){
$('.parallax-window').parallax({imageSrc: 'STYLESHEETPATH."/img/header-rivista.jpg"'});
});
</script><?php
}
?>