Other than fairly innocuous topics, like the weather, I think the one topic that can almost always be considered safe is the work/job itself. If you think about it, it's the one thinkthing all coworkers within the same company have in common, and it's a topic someone new to the company should be interested, even excited, to talk about.
Some of the questions I was asked, when I was new, were about:
- Past work experience. I had none, so this died down soon, but people did tell me where they worked before or where they went to college, and I just listened.
- Company history and milestones. Think of questions like "Did you know that back in 2010 we...", and typically the person telling the story was directly involved in whatever the milestone was.
- My role and responsibilities. Some had no idea what my role in the company would be about, so they just asked about that, and those who had some idea asked questions to see if I was clear on my role, and offered advice when I was not.