ajax response -1 in wordpress theme

Pay attention that your ajax request will work only for logged in users. If you want to make it working for everybody, you have to add one more action wp_ajax_nopriv_myajaxpagination with the same hook:

function videospage(cnt)
{
    var pageno=cnt;

    jQuery.ajax({  
        type: "POST",  
        url: "<?php echo admin_url('admin-ajax.php'); ?>",  
        data: {  
            action: "myajaxpagination",  
            pageno: pageno,  
        },  
        success: function(datas){  
            alert(datas);  
        },  
        error: function(MLHttpRequest, textStatus, errorThrown){  
            alert(errorThrown);  
        }  
    });  

}

add_action('wp_ajax_myajaxpagination', 'my_action_pagination');  
add_action('wp_ajax_nopriv_myajaxpagination', 'my_action_pagination');
function my_action_pagination()
{
    $pageno=$_REQUEST['pageno'];
    echo $pageno;
    die();
}

Read more about AJAX in WordPress.