The vagent command with the -V or --version flag can be used to display the version of vagent that is installed.

/opt/venafi/agent/bin/vagent --version

Something like this should be returned.

Venafi Agent v20.3.0-20371005
    Architecture: 64-bit
       Root path: /opt/venafi/agent
     Binary path: /opt/venafi/agent/bin
    Library path: /opt/venafi/agent/lib
    Drivers path: /opt/venafi/agent/lib/drivers
   Database path: /var/opt/venafi/agent/data
  Temporary path: /var/opt/venafi/agent

Venafi Agent Loader Library v20.4.0-20471145

Venafi C Portable Runtime Library v20.4.1-20481276

Venafi Agent Config Library v20.1.0-20170698

Venafi Agent SSH Management Library v20.3.0-20370927

Venafi Agent Certificate Management Library v20.2.0-20270961

Venafi Agent Library v20.4.0-20471161

Module(s)
    VED Agent KeyStore Scanner Library (ksscanner) v20.1.0-20170739
    VED Agent Log Deliver Library (logdeliver) v20.1.0-20170698
    VED Agent DevOps Module (devops) v20.2.0-20270921
    VED Agent SSH Provision Library (sshprovision) v20.2.0-20270949
    VED Agent KeyStore Provisioning Library (ksprovision) v20.4.0-20471162
    VED Agent SSH Discovery Library (sshdiscovery) v20.4.0-20471179

Venafi Agent Sysinfo:
    Manufacturer: VMware, Inc.
    Model: VMware Virtual Platform

Venafi Agent Product Version: 20.4.1.0
Venafi Agent Product Date: 03/02/21 05:45:35