Green’s Dictionary of Slang

jojo n.

(US black) the penis.

a.1967

‘Stagger Lee’ in D. Wepman et al. Life (1976) 135: He hadn’t copped for a long, long time, / And he had to play with Jojo ’cause he didn’t have a dime.

In compounds

jojo book (n.)

(US) a pornographic book.

1997

A. Spiegelman in Adelman Tijuana Bibles 10: These old Jo-Jo books do have a liberating ‘any-port-in-a-storm’ polymorphous perversity.