Don't know VS Just don't know
In English we distinguish between "don't know" and "just don't know", with the latter usually meaning "it's simply that we don't know". For example:
"We don't know who's on the list."
"We know who's on the list. We just don't know what order they're in."
However, when I look up "just don't know" in a context translator, I'm given "Je ne sais pas..." Would "Je ne sais pas simplement..." or "C'est juste que je ne sais pas..." work for the distinction?