First of all be careful with SQL injection
$sql = mysqli_query("DELETE FROM comments WHERE p_id=$vrr");
Now let's get back to your problem.
var smt = $(this).closest("div").find("p").html();
Where is the p tag ?
add a p tag and will work, otherwise the p tag will always be null!!!
<div>1<button id="jqhide">Hide</button><p>some text to be sent via ajax </p></strong><br/></div>
<script>
$("button#jqhide").click(function(){
alert($(this).closest("div").find("p").html());
var smt = $(this).closest("div").find("p").html();
$.post("send.php", smt);
});
</script>