Don't run SLES but ... you need to find out how apache is running ... using mods or using fastcgi or what?
So, create a phpinfo.php file and put that file at your web server document root. Don't know where that is on SLES but on CentOS/RHEL that's /var/www/html/ - on SLES it's where ever currently have the moodle code.
In the output of the phpinfo.php file look for:
Loaded Configuration File ... which shows the path to the php.ini file it's loading.
Scan this dir for additional .ini files ... which shows the directory PHP will look for to parse additional ini files that configure PHP extensions.
Additional .ini files parsed list the files in the above additional directory.
IF you see /etc/php.d/opcache.ini in there it's that file that one needs to edit to configure zend opcache.
Normally, the very first line of such an ini has an 'enable' line ... 1 for on ... 0 for off.
Also, which file to edit also depends upon how your apache is setup ... using loadable modules? FastCGI or ?
https://www.suse.com/documentation/sles11/book_sle_admin/data/sec_apache2_configuration.html
IF I re-call correctly, one should use whatever method one had used before ... YAST ... to configure services, etc..
https://www.suse.com/documentation/sles11/book_sle_admin/data/sec_apache2_modules.html
So once you find what ini files are being used and how apache is being run, go back to those files you edited and revert them to their original state.
Remember that editing in SLES might best be done in Yast.
Don't forget to restart apache service after making changes to config.
After restart, check apache logs to see if it's complaining about anything.
'spirit of sharing', Ken