Adding individuals' event attendance as activity for employer?
There are a couple of ways to do this:


When creating an activity, add the Organization as a related contact.
Create an extension to automate adding the Organization (see below).
Create a custom report (not recommended).


As extensions go, it's pretty easy to write:


use the hook_civicrm_pre to hook created activities.  
Use an API call to look up the contact.  Is the contact_type equal to Individual? Is the employer_id not null?
If so, add the employer as a related contact.


You'll have to consider edge cases: What happens if someone leaves an organization - does their attendance still count?  If someone joins an organization after the activity, does that count?  A custom report limits your ability to handle edge cases any way other than a "default" way, which is why it's not usually recommended.