"What could Luke be doing though?"
I have no idea, I just want him to be doing it.
He's probably doing exactly what anybody else would be doing in reality, he's basically a refugee with no power, in a foreign country, having to fit in with their red tape, and without contacts back in Gilead and no idea if June or Hannah are alive or not.
Obviously Moira knew up to the point of her escape, but things change very quickly in Gilead and people are killed on whim for the most flimsy reasons.
So I know it's unfair but I can't help it, I want to see him fight for them, even though realistically there's not a massive amount he can personally do.