[Plugin: W3 Total Cache] how to see if a page is cached in memcache

Not sure is this will work with memcache, since it is made for memcached, but you could give it a try.
https://dealnews.com/developers/cacti/memcached.html

I also found this script which the author ported from the APC.php script. https://livebookmark.net/journal/2008/05/21/memcachephp-stats-like-apcphp/

Alternatively, if you wanted to use APC instead, depending on your setup, it has it’s own php script. https://www.electrictoolbox.com/apc-php-cache-information/

thanks, will check those out

It’s also reliable to see if the date in an HTML comment in the footer of a given page is always changing, if so, that means that the page is not being cached or that you’re logged in.