How do I use my own knowledge in a Section A source analysis question?

You should use your own knowledge (OK) about the question as a lens through which to analyse the four sources. Instead of simply deploying OK to answer the question directly, use it to examine the provenance and historical context of the sources in order to evaluate their historical credibility. You could analyse their authorship, the date and circumstances in which they were written, style of writing and the purpose for which they were written (you won't have time to do all of these for each one - pick one or two of the most important factors) in order to make a judgement about how valid the opinion in the source is. You could use OK to group sources together and show how their similar context cause them to lead to similar conclusions.
Remember to use OK in a nuanced way - it's easy to pick apart sources and attack them for what they don't tell us. Better candidates will be more subtle and show how their OK interacts with the sources to challenge or support their views. Your conclusion to the question must be directly driven by the content and argument of the sources but the best candidates will use their own knowledge to come to a nuanced and original conclusion. Most importantly be bold - arrive at a firm, confidently argued conclusion.