Hi
You will need to add privileges Global.Diagnostics as documented in vSphere 5 Documentation here - View System Logs: vSphere Documentation Center
You can clone the built-in Read-only role then rename to something like Audit Role.
Edit the audit role, add privileges Global.Diagnostics as shown in screenshot below
Thanks,
Bayu
Bayu Wibowo | VCIX6-DCV/NV
Author of VMware NSX Cookbook http://bit.ly/NSXCookbook
https://github.com/bayupw/PowerNSX-Scripts
https://nz.linkedin.com/in/bayupw | twitter @bayupw