You can check if an event is server-side or client-side by grouping by Source from either the Usage over time chart, or the Analysis Preview section of the event’s details page. Source is a built-in session property.
To look at an individual labeled event, navigate to Data > Labeled events and search for the event you’re interested in. A pop-up will open, which includes an Analysis Preview section. If the definition is client-side, the result will be web.
If the event is server-side, the result will be server.
if you have two separate events that represent the same interaction, ex. a client-side purchase event and a server-side one, you set up a combo event to view these as one event.