Had a look at some notes....
This is tricky really because are you talking about the mach wave or the specific bow wave that appears to differentiate from the other shock wave at the trailing edge? (that trailing edge shock is the one that moves back from the point on the wing with the greatest acceleration as the aeroplane accelerates. Mcrit)
The mach wave will appear at 1.0M. On a "normal" wing not really designed for supersonic travel, it will attach at about 1.3M.
I am sure the aerodynamicists will rush to your help.