You can look at the properties to the Telligent.Evolution.Extensions.Calendar.dll or run /ControlPanel/dump.ashx and look at the same value from there
Development Lead- Extensibility
From: VinayakLSP [mailto:bounce-VinayakLSP@communities.telligent.com]
Sent: Tuesday, February 19, 2013 9:40 AM
Subject: [Telligent Evolution Platform Discussion] Event Calendar Version Information
How to determine the Event Calendar Version installed?