You can have a look at the package install history in the Core database
under /sitecore/system/Packages/Installation history/E-mail Campaign Manager
. If you have installed multiple versions then there will be multiple child entries with each revision number.
If you need to get the current running version from code then just get reflect the FileVersionInfo
var assembly = System.Reflection.Assembly.LoadFrom("Sitecore.EmailCampaign.dll");
var fvi = System.Diagnostics.FileVersionInfo.GetVersionInfo(assembly.Location);
string version = fvi.FileVersion;