She's shown twice making clandestine phone calls and in one case, getting a very conveniently timed dossier to whet the appetites of the remaining "Hunters". The question is, a mole for whom?
Considering the ending where they received a file from the person Harriett called, there's a good chance that there's a much bigger group of Hunters that exist, and the group we've followed was only focused on America and, with the exception of Harriett, is not aware of this larger group (and may not be informed of it until next season).
Why did Harriet's friend ask about Jonah? What about him is so important?
It's the only way the timeline makes sense (unless you take Writers Cannot Do Math into account). If Jonah is nineteen years old in 1977, he would have been born in 1958. If Naomi, his mother, was born in 1945, that means she would have been thirteen when she had him, which makes her death especially sad.
But now here's the real sad kick in the gut: did Naomi consent to the sex, being in love with someone and then the guy tossed her away or was she raped? Either option is not a good one.
If she was a young teenager she couldn't consent. Underage people aren't able to, at least legally speaking, because they're too young to make those kinds of decisions. Even if she wasn't technically forced, that's still statuary rape (probably).
The Wolf killed Ruth
As of the Season 2 finale, confirmed. She found out he was posing as Meyer, and so he had her killed so his identity wouldn't be blown.
Roxy will join Millie's taskforce
Given her daughter is still a priority, Roxy might want to stay stateside while the others go to Europe. Millie might have tried to recruit other Hunters, but they're already on the way to Europe.
Jonah is more than just Ruth and Meyers grandson
Why did Harriet/Rebekahs' contact in the season finale ask after Jonah? Is he just that interesting due to his intelligence and his quickly developing ruthlessness? Or do they know/think something about him that is yet to be revealed?
Travis Leich's Incident in Skokie referrs to Historical Court Case
happened around same time as the story set in. This caught the attention of Fourth Reich and got one of its members, Travis joined.