Competency in: This is the most common preposition used after "competency" when referring to a specific skill or area of expertise.
* Example: "She has a high level of competency in graphic design."
Competency for: This preposition is used when referring to a particular task or role.
* Example: "He has the competency for this demanding position."
Competency at: This preposition is used when referring to a particular activity or level of skill.
* Example: "He demonstrated his competency at problem-solving."
Competency with: This preposition is used when referring to a specific tool or technology.
* Example: "She has competency with Adobe Photoshop."
Competency on: This preposition can be used when referring to a specific topic or subject.
* Example: "He has a strong competency on cybersecurity."
Ultimately, the best preposition to use depends on the specific meaning you want to convey.