The following information is gleaned from comments and research done by David Dodd (quoting Blair Jackson's GOING DOWN THE ROAD) in his THE COMPLETE ANNOTATED GRATEFUL DEAD LYRICS pp. 276-77.
Iko is a slave song dervived from two chants into a call and response. In the late 18th century whites began to allow slaves one day a week "to strut their stuff and whoop it up in New Orleans' Congo Square while the gentry watched." This led to a competition between the various factions of singers and dancers which becomes the origin of the "tribes" which can still be seen in Mardi Gras parades. These competitions led to actual fighting till the 1890's when order was restored and the competition was confined to style, wit, costuming, etc. The lyrics of "Iko" show the vestiges of this change. "My spy boy," for example refers to one designated to alert his "tribe" when rival tribes get too close.
Accd to Art Nevilee of the Neville Brothers "I think it's a case of where the pronunciation changed over generations. It was 'Iko' by the time it got to Cheif Jolly. It may have come from the word 'hike,' because that's what you do on Mardi Gras -- hike all over the city, trying to see all the masks and the different parades."
The first recording of "Iko" (called "Jock-o-Mo") came from a young New Orleans singer named James "Sugar Boy" Crawford for Checker Records in 1954. Crawford says, ". . . to be honest, I didn't, and still don't have any idea what the words mean."
Next version is the famous one by the Dixie Cups (1965). This was an afterthought at a recording session when Phil Spector heard the singers and percussion jamming through the tune, he turned on the tape recorder and captured the track. Dr. John (Mac Rebannack), The Nevilles, and Grateful Dead are keeping the song alive through their performances.
So what does Jocko mo fee na nay mean? The exact translation is lost in time, but it was probably a mild insult in a disguised patois created so that observing whites could not understand it. Phil Lesh of Grateful Dead felt it meant "Kiss my ass." We may never know for sure.
Doug Saum (P. S. My two cats are named Iko and Jokomo.)