I can't find any Quick Look cache data in macOS Mojave beta I'm using macOS Mojave beta and I'm trying to find out where Quick Look cache data is stored.

As of High Sierra, I found the Terminal command to open the path of Quick Look cache data:

open $TMPDIR/../C/com.apple.QuickLook.thumbnailcache/


This is what it looks like:


But when running Mojave beta, my Mac doesn't have any files in that path (I haven't cleared the cache at all and checked with qlmanage -r enable), I frequently used Quick Look though.



Quick Look works fine but I'd like to know why my Mac doesn't store cache data.

UPDATE

This is the output of command:

sudo lsof -c quicklookd




But I don't see anything in the directory via Finder.

/private/var/folders/ff/3m1y9syj5cd_vhjpgy0yy5c00000gn/C/com.apple.QuickLook.thumbnailcache/


If I tried it through Terminal. It says the issue in terms of permission. I have completely no idea what this permission comes from:

~ (166) $cd /private/var/folders/ff/3m1y9syj5cd_vhjpgy0yy5c00000gn/C/com.apple.QuickLook.thumbnailcache
cd: error retrieving current directory: getcwd: cannot access parent directories: Operation not permitted

/private/var/folders/ff/3m1y9syj5cd_vhjpgy0yy5c00000gn/C (171) $ls -l | grep quicklook
ls: com.apple.QuickLook.thumbnailcache: Operation not permitted
In Mojave, quicklookd stores the information in the same private folder hierarchy:

/private/var/folders/&lt;id&gt;/&lt;random&gt;/com.apple.QuickLook.thumbnailcache


as in High Sierra.

To list the exact folder name used in Mojave (this procedure also works in High Sierra), open a Finder window, select a document or application, press space to fire up Quick Look, launch Terminal and run:

sudo lsof -c quicklookd


lsof -c displays which files and folders are in use by a specific process. 
The result will look similar to this (the red circle highlights the private folder):



The folder can't be accessed, neither by a standard user (even with sudo) nor by an administrator:


As you posted in your comment, the reason why you can't see its contents is because it is protected by System Integrity Protection. That's new in Mojave.