There's two, the CityWalk entrance on Universal Studios Blvd, and the other entrance is on Universal Hollywood Drive, which you can get to from Lankershim Blvd. I'm not sure if you can directly enter Frankenstein parking from that same path, but if you can I get the feeling you'll have to pay the preferred parking price if you want to park there.
In simpler terms, I would take Universal Hollywood Drive if you want Jurassic Parking, which is still relatively close. I've never taken that path because I had no idea it supposedly sends you there automatically. You're more likely to get sent to ET or Curious George if you take Universal Studios Blvd.