Answer: Expertise
Explanation: Expertise is a specialised skill or knowledge of a learned person in a particular field of study.
It is used to describe a skill in a specialised field of study. Expert skill can be in any filed of study such as Engineering, Programming, Medical field etc.
it is used to describe an expert in a particular field of study. and it is used to describe a knowledgeable person and a amateur in any field of study.