I don't think it's hidden desires per se, just that it strengthens the desires they have and bend them in a way that benefits us. Before we used the power on Jessica she wasn't exactly hiding how she felt about us.
Didn't word it properly. But it's around the ballpark.
Quoting Gramps.
"AWAKEN allows you to, well, awaken dormant desires, ideas and even abilities."
"Like Control, it binds people to you. They will come to love you, even worship you, over time."
{...}
"For now, you will need to slowly draw your target's desire, idea or ability to the surface."
"Then, and only then, will AWAKEN be able to take hold."
They're not exactly hidden for the most part, some of them are quite an easy guess once you read a bit into the character.
Some of them are not. Luna wanting someone reliable, powerful and dominant. Or Julie having daddy issues.
Not all the times we've used Awaken have had a desire pop up, or needed a desire to begin with. But it seems to be something you might want to have for it to have an actual effect.
For example we used it one to calm down Kana when she got too horny (When Kana is in heat and you don't want to bang her, pretty much the only time we've actively used Awaken on her except for the time it misfired).
I'm pretty sure when we unlocked the Nexus point at Gramps' place that was learning to Nexus from anywhere. We can't actually do so because game mechanics, but story-wise I'm pretty sure we are supposed to be able to.
I kinda see where you got that idea. But nah, sadly that isn't the case. Maybe in the future?
But for now we need to go to a place that has a "nexus point".
Morgana's place has a crystal and the other council girls' demesnes have some thing that acts as a access point.
The keys can warp us to places but if we don't have access to a point in there we will be warped back.
Somehow Gramps, or something in Gramps' place is a nexus point.
Did the old geezer eat a fucking nexus crystal?
It wouldn't be unheard of. People think he's "The First" and if he is then he lived before Artifact was even a thing.