How to respond, safely, to a student's 'risky' email?
If you want to be completely safe, I would answer something along the lines of: "This is outside my area of expertise. I recommend that you consult the career center on campus (insert contact information to career center)".

If, however, you want to actually give them advice, I would give it in a very neutral manner, where you could substitute every mention of "adult videos" by "video of student kicking a puppy" (or other potentially career damaging Google result). If you keep it on that very professional, neutral level, it shouldn't get you in trouble (note: I'm not a lawyer). Write your response, and then try the "puppy kicking test". If the email still makes sense, you're probably (again, I'm not a lawyer) safe.