Usually (I haven’t seen any of the newer ones up close) there’s an upper and lower urethane bushing of some sort in the steering shaft- upper or lower, take your pick. Sometimes they’ll crack/snap/wear and dirt/crap/whatnot will work in the bushing/rod surface and squeak. Put it on a stand and turn the handlebars back and forth - if the suspension’s unloaded and you still get the squeak, probably steering related.
You could pull apart the lower (more than likely) bushing/rod assembly and clean it out/replace the bushing, or - pretty much the same as everyone else said - spray the crap out of it with wd40. It’ll be good for a little while, probably have to spray it after every wash, since more crap will get in there every time you ride it.