He should ask his PO up front, no reason not to. Given that California has roughly a 75% recidivism rate for parolees, the odds are very much against him from the start, no reason to make it any worse. There will be a lot of conditions set up front, no guns/drugs/booze (or anything else fun), trying to find a job, AA/NA meeting, anger management etc. that will be absolute requirements, the knife collection question is more subjective and instead of lying or hoping for the best just ask up front and act accordingly.
Also, keep in mind that while on parole, you basically have no rights especially in the context of the 4th amendment. In normal speak, that means that he will not have the usual protections from warrant-less searches of his home like someone not on parole does. Basically, if his PO shows up at his home and says "let me in, I'm searching right now" he has to comply, refusing to do so is usually enough to land him back inside on its own.
In short, parole sucks...my close friend is a criminal defense lawyer and makes a VERY good living, mostly on repeat customers.