I watch this show.
FYI, the season was filmed SUMMER 2012, so if they were ever filming in or around TRENTON, it was not recent. But I don't think they ever filmed in NJ. The whole reason shows film in Canada is because it's cheaper (tax incentives, cheaper labor). I can't imagine they'd pick up the whole production and travel 500 miles to Trenton just to film 1 episode. I also highly doubt that Trenton PD would allow their vehicles to be driven 500 miles/8 hours one way to Canada for filming. Although, if they had NJ State Troopers driving them in a Death Race II caravan, they could probably make it in 4 hours.
Anyway, the license plates are probably stick ons. TV shows do this all the time. I'm betting the Trenton PD logos are stick ons too. Something like that is not that hard to reproduce. Especially for a special effects team like the one employed by this show.
As far as any hope of seeing NEW JERSEY locations (real or faked) in any of the storylines, NO, NJ definitely is not the location of a main storyline. If you're only watching tonight's episode in hopes of catching NEW JERSEY on the screen, you're gonna be disappointed.
There is a main plot running through all episodes so far (probably will run through to at least the end of this season). This main plot centers around a key serial killer out of MINNESOTA. A couple of the episodes so far have focused solely on this main plot. Other episodes are centered on a 'killer-of-the-week' subplot. It looks like tonight's episode is one of those, and so far it is the first mention of NEW JERSEY anywhere (I'm guessing probably also the last).
Other than that, the show is anchored in the D.C./VA/MD area (Georgetown U, Quantico FBI Academy, FBI Behavioral Analysis Unit, etc. etc.).
Personally, I would wait to watch it until after viewing Episodes 1-3, and also the 4th episode "Ceuf" that was pulled off the air at the last minute because of what happened in Boston and Connecticut ('webisode' snippets of this pulled episode are available on the NBC website). A lot of major, foundational plot and character stuff has been laid down. At the very least, you're not gonna know what's going on when they mention things from the main plot. If you haven't DVRed Episodes 1-3, they are available to watch online on the NBC website. The episode airing tonight will also be posted in the next few days, so you don't have to worry about missing it.
However, if you're gonna jump in and start watching in the middle of a season, a 'killer-of-the-week' subplot episode would be the place to jump in, I suppose. But like I said, NJ and TRENTON are not major elements to the story.
As far as TV shows and movies that HAVE been filmed in NJ, here are some links:
NJ Motion Picture & Television Commission
https://www.facebook.com/NJFilmCommission
Television and film in New Jersey - Wikipedia, the free encyclopedia