He'll probably talk for a while. If there's a moderator that mod will ask you questions. The audience usually asks questions. The comic book guy might include you on his own. ... Ask someone who knows.
I was on a panel once and this was essentially the format it took. Introductory comments by the moderator, we each got to introduce ourselves, the moderator asked questions, and then the audience asked questions. Afterwards, there was some casual networking.
The people who organized the panel should at least be giving you the format of the panel before you appear. If they haven't volunteered this information, you can request it.
Here is an example of a game dev panel (it essentially takes the same format as the one I described above):