Sorry, but going to Knowsley Safari Park by public transport might be a bit pointless. To see the animals you have to drive round the park in your own car. Some safari parks used to operate minibus services for those without cars but these seem to have been discontinued at most (possibly all?) such parks. The absence of any transport facilities around Knowsley Safari Park is confirmed here:
http://knowsley.com/s_park/faqs.asp
However, some attractions are available to pedestrians. This is confirmed by the availability of a �7 admission tickets for pedestrians:
http://knowsley.com/s_park/timesandprices.asp
(That compare with the �12 price for adults in cars and reflects the fact that you'll miss out on the 'safari' element of your visit).
The 10 and 10A bus services, which run frequently between Liverpool and St Helens will take you to Brookbridge Garage on Liverpool Road. From there. it's about a mile's walk. To plan a route from your starting point, use the facility here:
http://nw.aimwebsites.co.uk/JourneyPlanner.jsp ?vm_Reset_str=true
Chris