I had looked at this very early on when evaluating Zenoss, and the take away was it just wasn't the right tool for the job. Even with a custom report, its not going to be easily searchable.
What I would suggest is that you manage the knowledge in a wiki or some other tool. When resolving an event link to the wiki, rather than typing the solution in the event log.
Keep in mind that the events are stored in MySQL. This means in theory you could wrap some sort of searchable interface around some MySQL queries, but I wouldnt suggest this. Events can take up a ton of space, and its typical to have event aging enabled so that older events are purged, keeping your mysql db size down. If you were using it for knowledge, it would get dicey because you would probably want to keep knowledge around a lot longer than events.