Jason Mendoza was an amateur practitioner of what music-related job?

Jason Mendoza was an amateur disc jockey, or DJ, before his death.

Jason is introduced to the Good Place under the false identity of Jianyu Li, supposedly a silent Taiwanese Buddhist monk. The disguise works partly because he agrees not to speak, but his real personality eventually emerges when he reveals that he is Jason, a drug dealer and amateur DJ from Jacksonville, Florida.

His music-related ambition is treated as both a character joke and a genuine detail. Jason specializes in electronic dance music and dreams of making a living as a DJ, even though his self-description as a “professional amateur” underlines his lack of conventional success.

The answer is not radio host or music producer: Jason performs and mixes music rather than presenting broadcasts or creating studio recordings. His DJ identity also reinforces the show’s contrast between the harmless persona he pretends to be and the impulsive, immature person he actually was on Earth.