Here's a breakdown:
* When "DJ" is a job title or a noun referring to a person: It is not capitalized, just like other job titles like "teacher" or "doctor."
* Example: "The DJ played great music."
* When "DJ" is part of a proper noun (name of a specific person or group): It is capitalized.
* Example: "DJ Khaled is a famous producer."
* Example: "The DJs of Tomorrow competition was exciting."
* When "DJ" is used as an abbreviation for "disc jockey" in informal writing: It is not capitalized.
* Example: "I want to be a DJ."
In doubt, it's always safer to err on the side of not capitalizing unless it's part of a proper noun.