the jet needle is the needle that hangs down from the carb slides. you get at it by pulling the tops off the carbs, popping the slides out and dumping the needle out. watch out for washers, shims, and other little bits. some carbs have little o-rings on the tops too. watchout for those as well. you can do this with out removing the carbs, generally, but you have to pull the airbox usually.
The needle jet is also called the emulsion tube. its the brass tube that the needle runs into in the bottom of the throat of the carb. its usually pressed into the plastic slide carrier and has the mainjet screwed into the bottom of it. this is not an adjustable part, but can be worn sometimes and may need replacement. you'll have to pull the carbs to fiddle with the needle jet/emulsion tube.