Hello,
there are many people named Zakotnik in Lubljana (even my coworker:). If you could give more detailed information (where in Ljubljana, what kind of building, how or where was it written) that could help. Can you find any old documents that person brought from Ljubljana? Maybe a photo? Try to give us as much you can find.
Even if we can't help you with this specific building, we'll do our best with your additional questions about Ljubljana. You'll enjoy being here. And since Slovenia is a small country, I recommend visiting more than just Ljubljana.