When setting up a live event there’s an option to tick for a attendance report. Keep in mind that if you are doing an external event, (outside org) anonymous join will be allowed, hence the user properties etc won’t be collected. You will then only see how many, the name they choose to put in and so on. If you need more information than this you need to collect the data somehow. Most commonly this is done during a registration process for the live event like creating a registration form that collects the information. There’s no proof that they actually will join the event though. This information can then be used for follow-up etc.