Green’s Dictionary of Slang

james earl dog n.

[? ref. to James Earl Ray (1928–98), the alleged killer of Martin Luther King in 1968]

(US campus) a marijuana cigarette.

[US]Eble Campus Sl. Oct.
[US]Eble Sl. and Sociability 70: Dog is often the second member of a compound or phrase: [...] hooch dog, jimmy dog, james earl dog ‘marijuana cigarette’.