How can I jack a steel post out of the ground?
I would use a chain and make sure it is bolted to the post so that the link  is touching the post, (both sides ) I.E. threaded bolt through the link with a nut and washer holding it tight to the post. Do this on both sides of the post so you create a loop for the jack to pull up on. You may want to rent a hydraulic  post puller.