I have tried everything you have mentioned. Still no luck. I m wondering why I m getting this empty page even I removed .htaccess file. And I tried turned on all php error/warning but still nothing on the page.
Just checked your https://online.readingrescueontario.info/ and the host answer is:
HTTP/1.1 400 Bad Request
I'm assuming that this is an Apache's config issue.
You can check it by removing all Elgg files and creating a temporary index.html file:
<!DOCTYPE html>
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
<title>It's works</title>
</head>
<body>
Server OK
</body>
</html>
Then try to open https://online.readingrescueontario.info/index.html
As you are migrating your site (and not just restoring from a backup) you need to do what is described at http://learn.elgg.org/en/stable/admin/duplicate-installation.html including changing the relevant database entries to take intro account the different domain and possibly also different paths to Elgg install folder and data directory. Also, do not forget to flush the cache to not having any cached files still pointing to the old domain/paths. Just work through the instructions from beginning to end (or double check everything now that you have already started to migration). Also, do not update to a newer Elgg version at the same time as moving to the new server. If you tried that, start the migration again from the beginning with the backup of data directory, database and install folder as taken from the old server.
You might also want to check the Apache error log to see if there's some entry that might explain what's wrong. You should also check if the Apache config includes AllowOverride All for the install folder for the rewrite rules to work. Without Elgg's .htaccess it won't work for sure. And the .htaccess might require some adjustments for the new server location if you have made any changes required for the site to work on the old server. Also, does the subdomain work at all? You could test that with adding some test.html file to the root folder of the domain that outputs some text and then call this file directly in the browser. If the text is not shown the problem is not with Elgg but with the server config.
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