The "????" quest is the ahri quest.
To find the 2nd one, check the guild at daytime (There is a crystal tail on right), the 3rd will be in your room.
For 2B, you have to reach level 37, and check her in her room (A story trigger, she is talking with the console, there is an animation where some part of their body are transform in human skin)
Then you will unlock "Build a robot" quest, it's the 2B quest.
Thanks for quick reply. I've been checking the hub every day at daytime and I do not find the 2nd crystal. The first one I did find. Since I did not find the 2nd, there has yet to be a third.
Regarding 2B quest, I am level 37, and I got a scene when talking to the console etc... however nothing came of that. Not sure exactly why, no new quest, nothing.
Edit: Now got every scene for all girls (except 2B and Ahri which I cannot find / unlock) except for 1 scene with Marin which says needs continuation of story (no quests left to do and no more stars to do) and I think one other girl also had a similar scene as Marin that was locked behind story that doesn't seem to exist.
Edit2: I found the crystal and managed to find Ahri. It was NOT in the hub though. It was in the adventure guild.