How do I determine which version of VMware for Horizon client MacOS I need to download? I have a MacBook Pro and am running OS X El Capitan version 10.11.6
The release note of each Horizon macOS client release states the supported macOS versions.
Go to https://docs.vmware.com/en/VMware-Horizon-Client-for-Mac/index.html, and check the release note for releases.
BTW, why are you staying on an outdated system of 5+ years old (El Capitan version 10.11.6)?
Did you ask whoever supports the Horizon deployment that you would be connecting to?