Explain the brief history of both, as well as the advantages and disadvantages of both. Every technology has advantages and disadvantages. What types of files use one or the other? Compare and contrast them, and explain how they are used in modern times.
Here are some readings that might help you get started (search for more):
https://www.w3.org/blog/2018/07/the-world-wide-success-that-is-xml/
https://blog.logrocket.com/the-quiet-revolution-how-json-displaced-xml-1e1f3e8552f7/
https://sdtimes.com/communication-protocols/json-vs-xml-battle-format-supremacy-may-wasted-energy/
https://www.quora.com/What-are-some-of-the-best-uses-of-XML
https://towardsdatascience.com/interactively-analyse-100gb-of-json-data-with-spark-e018f9436e76
https://hackr.io/blog/json-vs-xml