Hi,
My contractor cut two intersecting post tension cables 
and repaired them with couplers. I am not sure how good the tension and repair are. Should I hire a structural engineer or house inspector to check?
Thanks for your help.
Go with an engineer that has experience with this technique.
I wonder if the contractor re-tensioned the cables after the repairs.
Brian’s spot-on about the Engineer Of Record (EOR)
The initial placement and tension of the tendons is a design decision that an EOR made. Any damage repair should comply with original design specs or addendums from them or an EOR you hire. You’ll want copies for your own records and to pass along upon resale of this property as part of the disclosure documentation, for integrity assurance, your own peace of mind and theirs…hth