Question: Living in Germany for quite a while now, working as an architekt, I stumbled over the word *Preisrichtertätigkeit.* Anyone a clue what this expression means?

Answer: 
A "Preisgericht" is a jury, mainly in the context of sports and arts. A "Preisrichter" is a member of such a jury. "Preisrichtertätigkeit" basically means that somebody works or worked as a "Preisrichter".
It means being in a jury for a contest in which the participants (or one of them) get prices.

Preis = price,
Richter = judge,
Tätigkeit = activity, occupation