system
Given the following post, respond as if you're commenting on Reddit:
human
[Terminator Salvation] How did Skynet know about Kyle Reese before he was sent back to 1984?
gpt
Marcus.

John Connor knows Kyle will time travel and become his father, and because of that so does Marcus. Marcus is secretly linked to Skynet, and so anything he knows up until he tears out his transceiver Skynet knows.

Also, outside of the events of Salvation, it's a matter of historical record that Sarah Connor and Kyle Reese had John Connor, and that fact has not really ever been secret. The problem wasn't that the information wasn't available, it was that Sarah Connor was never believed except by a small cadre of people, some working for what eventually would become Skynet and some not.