There is a 'Triggers' log event to be used in the Db.LogEvents application settings to enable trigger-related logging:

 . . .

  <add key="Db.LogEvents" value="Errors,Main,Triggers" />

  . . . 

when this logging is enabled the system generates entries in the main log file (typically GN4.log) every time the triggers are loaded from the databasse:

  . . . 

  /*

    Loaded 989 triggers in 64ms, memory usage: 43 KB

    2010-11-17T23:24:51.277+01:00

  */

  . . .

and every time a trigger fires:

  . . .

  /*

    Trigger 'folderObject.folderRef referencing obj9', cause 'SendFrom obj1787':  scheduled workflow 'testtrigger' with task id 196

    2010-11-18T22:03:34.696+01:00

  */  

  . . .