Parking is always very rough from friday morning all the way through sunday night. Because NDK sells out all of the rooms for the hotel, and most of the rooms are for the entire weekend, the parking lot stays pretty full until the con is over. On friday if you show up early enough, around 8am-9am you shouldn't have a hard time finding a spot, but from then on till sunday night you really just need to get lucky.
Don't park in any of the lots around the hotel either, they do tend to get a little upset by that and have been known to tow away cars without a parking pass for those lots. My suggestion to you would be, find a parknRide and take the light rail to the belview station which is located just on the other side of the highway of the hotel. Then you can just walk over the bridge and you're good to go.