Getting to Knott's Berry Farm is very easy. Is one of the best connected parks. There are many ways to get there.
The park is now part of the Anaheim Resort Transportation service, so the easiest way is by a shuttle bus.
Other better option is by metrolink trains, the nearest station is The Buena Park Metrolink station, only a few minutes from the park.
For international visitors, there are two airports at just 30 minutes from the park: Los Angeles International Airport (LAX) and John Wayne/Orange County Airport (SNA)