Most post-tensioned slabs will have an embossing in the slab in one or two places, usually by the garage door saying something to the effect that this is a post tensioned slab.
You really couldn't miss them if they were there.
You will also have to prepare the cut concrete section like it was a new slab when you pour the patch for it. Drill and epoxy holes for rebar to connect old to new, compacted gravel and/or sand, 6 mil. vapor barrier, etc.
Thanks - I had not given much thought to closing up the holes, just making them.