brew cask install java6 - Cannot install on volume / because it is disabled - MacOS 10.15 beta
I found a workaround here: https://oliverdowling.com.au/2015/10/09/oracles-jre-8-on-mac-os-x-el-capitan/


  You can have it (Java6) installed without actually using it, however, it’s
  possible to trick the applications into thinking legacy Java 6 is
  installed, without actually doing so.
  
  If you’re running El Capitan, this is actually a little difficult now,
  because Apple added SIP (System Integrity Protection) to OS X. I have
  written a post explaining how to disable and enable SIP.
  
  If you’ve disabled SIP, or are not running El Capitan yet, you can
  trick some applications into thinking legacy Java 6 is installed by
  creating two folders with the following commands in Terminal:


 $ sudo mkdir -p /System/Library/Java/JavaVirtualMachines/1.6.0.jdk
 $ sudo mkdir -p /System/Library/Java/Support/Deploy.bundle 



  Don’t forget to enable SIP again after creating these directories.