I solve the problem, its my mistake...
<?php
include("includes/db.php");
if(isset($_POST['login'])){
$email = mysqli_real_escape_string($con,$_POST['email']);
$password = mysqli_real_escape_string($con,$_POST['password']);
$sel_user = "select * from jobseeker where email='$email' AND password='$password'";
$run_user = mysqli_query($con, $sel_user);
$check_user = mysqli_num_rows($run_user);
if($check_user==1){
$_SESSION['email']=$email;
echo "<script>window.open('home_user.php?logged_in=You have successfully Logged in!','_self')</script>";
}
else {
echo "<script>alert('Password or Email is wrong, try again!')</script>";
}
}
?>