To Jing a Jong translates to Smoking (or rolling) a Joint.
(In terms of rolling the joint)
"You gonna jing that jong bro?"
"Yeah, I'm jinging it right now"
(In terms of smoking the joint)
"Let's jing this jong"
"You're late. We just jinged a jong"
Note: The usage of this term does not necessarily have to include the full term, "Jing a Jong".