Derivied from the English phrase 'Whats going on, old boy?'. Now typically and commonly used in 'The ghettos' both stateside and in the UK. Can also be variated to 'Gwaanin' when used as a response to the question 'Wagwaan'.
Jamal enters the smoked-out low-rider. "Ah! Wagwaan!" says his homie with excitement. "Gwaanin?" he replies, "you be passin de dutchy on de left han side! Dat be gwan! Boyakasha!"