That depends how many days you want to spend in each park, I would give at least 2days for Knoebels. It's not a huge park, but it's bigger than it looks and you won't want to rush thru it. And you could probably use 2 days for Dorney, depending on whether or not you go into the water park part of it. Knoebels has their 2010 brochure and map for download at their website. Not sure about Dorney thou. As far as hotels are concerned, I would start with what park you plan to visit first and look at hotels in that area. A lot of hotels in central PA have very reasonable rates, just keep in mind that if you plan to stay in a hotel when visiting Knoebels, the nearest hotels are about 15-30 min from the park, and Dorney has some very close, but they charge more and the rates most likely go up on weekends. You might want to hit-up the visitors bureaus for each of the areas you are visiting and they can give you a good idea of what lodging to expect.
Here is the link for the area around Knoebels:
http://www.itourcolumbiamontour.com/visitorInfo/accommodations.aspx
http://knoebels.com/index.asp
And here is the link for the area around Dorney:
http://www.lehighvalleypa.org/visitors/specialoffers/travelpackages/dorney_deals
http://www.dorneypark.com/
Hope that's of some help to you.