It is a "Veranstaltung zum Gedenken" = "Event for remembrance".
"Gedenken" is an unusually flexed irregular verb, which is not commonly used — mostly in the aforementioned context. It is not a service, as that would imply a religious thing that you do in church, and that is "Gedenkgottesdienst" in German.
It is, instead, a public gathering to remember someone or something, and it usually includes a minute or so of silence (German "Schweige-" or "Gedenkminute") in which all attendees are supposed to think about the person or event that the remembrance event is for. The rest is mostly speeches, talking about the nice things one remembers about it — it's more similar to something that happens during a funeral at the grave, but more public.
I have to add that this is the traditional and well, literal interpretation. Nowadays, it can be anything, but it is a public gathering and you will most likely have that "Gedenkminute", but the rest is open to interpretation, which can mean anything that befits the person or event that is remembered, as chosen by the people. Depending on importance, it may also be broadcast.
as a comment, cannot comment due to low rep
in your case, I would say it's very likely they would include music from that person.