Xcache can be enabled in cPanel by using Easy Apache.

1. Log into your cPanel server
2. After you login, search for "EasyApache" in left column and click on the link
3. Select "Previously Saved Config" and click on "start customizing"
4. For both Apache and PHP, click on "next step" button
5. Look for "xcache for php" and check the box
6. Click on "save and build"
7. Allow the build process to finish
8. To enable xcache, you will need to make changes to php.ini before it can be used by your scripts.
   1. Login into your server using SSH
   2. After you login, enter "pico  /usr/local/lib/php.ini"
   3. Hold ctrl+W and search for "xcache"
   4. Make necessary changes and to enter ctrl+O to save the file
   5. Aftererwards you will need to restart Apache in WHM for changes to take affect

Here is recommended settings for xcache in cPanel --- 

xcache.admin.pass=""
xcache.admin.user="mOo"
xcache.cacher="On"
xcache.coredump_directory=""
xcache.count="1"
xcache.coveragedump_directory="/tmp/pcov/"
xcache.coverager="Off"
xcache.gc_interval="300"
xcache.mmap_path="/dev/zero"
xcache.optimizer="On"
xcache.readonly_protection="Off"
xcache.size="50M"
xcache.slots="8K"
xcache.test="Off"
xcache.ttl="3600"
xcache.var_count="2"
xcache.var_gc_interval="300"
xcache.var_maxttl="7200"
xcache.var_size="16M"
xcache.var_slots="8K"
xcache.var_ttl="3600"