Question: I am writing a paper and I am lost for a phrase to describe the set of topics a person is knowledgeable about.

For example: "If someone knows about topic A and also knows about topic B, then topics A and B are [phrase relating the topics and the user's state of knowing]."

Answer: 
Those topics can be said to be “*in his **wheelhouse***”

Defined in [Dictionary.com](https://www.dictionary.com/browse/wheelhouse) as:

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> within one’s area of expertise or interest:  
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> *There are some subjects that are in your wheelhouse and some that are not.*
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They are his or her specialities.

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> Specialty = a subject that someone knows a lot about
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> [Cambridge doctionary](https://dictionary.cambridge.org/dictionary/english/specialty)
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