This is where tags do come in handy.
If you know you might do something with a contact you met at a certain event, create a tag and notate on the contact.
If you think you’ll need to always know that contact was at the event, then either create some form of custom form, or have a standardized way of notating it.
In your case now, if you really need to know who came to Brisbane, you’ll probably have to look through each contact…. I don’t think Solve does broad match keyword search (or does it?) only phrase match.