New DM here; our group is in the very early stages of a D&D 5e campaign. My players have been hired to provide security for the wedding between Lord P (whose nefariousness was established in previous sessions) and Princess Q (the players know she is widely beloved, but little else). I've tried to drop copious hints about what's really going on: that Princess Q is also a spy whose goal is to learn what Lord P is up to.
My problem is that I truly can't tell whether the players have figured this out or not. No one has come out and said "oh, she's a spy!" But it could be that they consider this obvious enough that no one has bothered to repeat it out loud. (Right now the party is focused on figuring out whether Princess Q is in immediate physical danger, and from whom; this additional knowledge wouldn't necessarily have affected their actions yet.)
Knowing that Princess Q is a spy isn't crucial for the plot, but it would add interest to the story and could affect the party's choices later. I think the players would enjoy deducing this fact for themselves rather than being told straight out, which is why I haven't been more direct; it also wouldn't be realistic for these low-level characters to be told explicitly about high-level espionage operations.
I ask the players for a summary at the start of each session, to remind us of what's happening and let me assess what they think is important. But I don't think I can ask more specifically without giving things away if they haven't in fact figured it out. ("So, what do you guys think Princess Q is up to?" is pretty suspicious.) How can I probe what my players have and haven't figured out, in a way that isn't too obvious?