I know the answer ^? i heard he's on the shield world onyx.
Status unkown. He was last seen escorting Dr. Halsey to CASTLE base. In Halo: The First Strike, the Spartan IIs discover her there alone very soon after. This leaves two options for Jun: He died getting her there, or, upon delivery, was reassigned to another mission or evacuation. There is no Official Halo canon explanation of what happened to Jun.