The Last known information should be fine. I believe if you don’t know it, there’s a box for that too. I would say it wouldn’t warrant re establishing the relationship if there isn’t one to find out. But at least put in the effort to google him. It will come up in your interview, and if you can explain it, it won’t be an issue.I know this threads a little old but I didn't see a newer one when looking around on this topic.
I'm mostly just worried about section 18. Information on immediate family and in-laws.
My parents divorced when I was 8 years old. I haven't had contact with my biological father since then. Do I need to track down his info for this?