A pragmatic approach mentioned in only one comment:
@markus, a more realistic solution here other than "you'll all go to jail for reading the document!". Could you very simply strike up a conversation with the nice old lady What about "I saw from the telephone number you're sending something to Nigeria, say I visited there once" With luck she'll just immediately start telling you the whole thing. Then you can all just chime in "OMG, you're being scammed, I just saw a story about that on TV" and then show her some scam articles. You know? Why not do that? – Fattie 5 hours ago
A nice old lady who falls for a Western Union "send us money" scam is overwhelmingly unlikely to prosecute you for having...what, exactly?
You noticed the content of the paper she handed to you.
Kinko's workers aren't robots. IANAL, but it would be absurd to expect someone not to notice ANYTHING about the paper they are copying. Granted, I could imagine situations where legal action against a Kinko's worker could make sense, but those would be in the realm of discrimination or fraud.
Example: discriminatory remarks made when someone hands you a promotional flier for a religious group to be copied. Example: taking note of confidential information such as an SSN from a document and then using that.
In neither of these cases would the litigation be for having just noticed what was on the paper. Instead, it would be for other forbidden activities that were prompted by what was on the paper.
This isn't legal advice; just common sense.
Advising the nice old lady that she may be being scammed would be a very nice thing to do. The only aspect remaining would be, how best to do so?
I would imagine a conversation something like so:
You: Excuse me, I couldn't help noticing that you are often making copies of Western Union money sendings?
You: Well, I don't know if you know this, but I just want to be sure you're warned that there are a lot of scams going on today that use Western Union as their way to get money from the people they're scamming.
See what she says to that. If she angrily tells you to mind your own business, fine, at least you tried. If, as is far more likely, she expresses some interest or "I didn't know that," you can say/ask:
Yes, it's very common. So it's important, before you send money to someone through Western Union, that you have done some research on the company or person you're sending money to. For example, do they have a website? Is the company a real company? If you look on the internet for "company name scam" or "company name legitimate," you can usually find people who've had the same question and share their experience.
You seem like a very nice lady and I'd hate for you to lose your money to a con artist. Perhaps you have a relative who could help you look into it.
My advice is, go for it.
(Aside: It's sad that we live in a world where people are afraid to help other people for fear of litigation against utterly well-intended actions. I, for one, don't want to live in such a world. I will help people regardless.)