Etiquette of introducing yourself to a professor I am writing my master thesis at a university in Germany. I am looking into universities and institutes where I could carry out a PhD. One of the possibilities I have been looking into is a group at an university from Switzerland.

This group’s head will be tomorrow at my university, acting as a second examiner at a thesis defense. I think this is a good opportunity to introduce myself personally and maybe ask about the outlook of doing a PhD at his group.

What is the ettiquete in such situations? I think it is not uncommon to find yourself in an academic event with someone you are interested to work under.
Your best chance is to get one of the other examiners who is local to your university to introduce you. It would be better if this could happen at a social function (dinner, drinks, party for the newly minted PhD, etc), i.e., somewhere you might get a few minutes to actually talk. It would be best if your local acquaintance would pave the way with an email and some chit-chit so that you have a clue whether ProfZ even has a position available. 

If you can't get someone who know you both to make an introduction, then you'll just have to walk up and introduce yourself. It would be better to have figured out in advance whether there is a position available or not, but it's getting a bit late for that (try anyway). If you can, you still might send ProfZ an email today introducing yourself and asking if they have a few minutes to talk about possible PhD positions at UniY while they are visiting.