I'm sorry if this question is too novice. It comes from a practice midterm in a cryptography course which I'm taking, and my confusion here is really that I don't know the "tools" that one uses in practice for this sort of question. The notation (and class) is Katz's.
I've been given a PRG $G(s)$; I'm trying to show explicitly that $s\mathbin\|G(s)$ is not a PRG. Intuitively, I'd expect both components to be random-seeming, so there's nothing obvious that sticks out to me to XOR or manipulate.