How should I ask what degree abbreviations an academic wants to come after their name?
[Expanding @Thomas's comment into an answer, so the question may be resolved]

The best way to figure out how a person would like their name listed is to simply ask them directly, as opposed to attempting to infer it from their biographical information.

Thus, when you are putting together the program, name tags, etc. let the form have a blank saying something like:


  Name, as you would like it to appear in the official conference program


Note that sometimes people want something different on their badge and on official listings, so it's worth having two blanks if you are asking about badges as well.