use global scope on your $con and put it inside your getPosts() function like so.
function getPosts() {
global $con;
$query = mysqli_query($con,"SELECT * FROM Blog");
while($row = mysqli_fetch_array($query))
{
echo "<div class=\"blogsnippet\">";
echo "<h4>" . $row['Title'] . "</h4>" . $row['SubHeading'];
echo "</div>";
}
}