This criterion effectively evaluates how well you demonstrate content knowledge and understanding of the key issues, debates, theories, and arguments that surround your chosen topic.
It also measures how fluently and accurately you use the command terms (or terminology) and concepts of your chosen subject. This also includes demonstrating knowledge of any subject-specific modes of analysis, preferred methodological approaches or styles and any evaluative or interpretative frameworks.
Lastly, high marks in this criterion are awarded if the choice of resources is consistently relevant and befitting of an academic research paper in the chosen subject.
From the IB Guide:
IB Command Terms can be helpful thought starters, and can guide you to forming a good research question. Try to incorporate an IB command term in the research question if possible.
The work does not reach a standard outlined by the descriptors.
Knowledge and understanding is limited.
Use of terminology and concepts is unclear and limited.
Knowledge and understanding is good.
Use of terminology and concepts is adequate.
If the topic or research question is deemed inappropriate for the subject in which the essay is registered no more than four marks can be awarded for this criterion.
Knowledge and understanding is excellent.
Use of terminology and concepts is good.