Generator for Running a Spot Welder?

The amps on any wire is determined by the voltage and the load that is being served. If you are asking what is the maximum current allowed on a #8 AWG, that would be 40 amps for a 60 degree Celsius rated wire, 50 amps for a 75 degree Celsius rated wire and 55 amps for a 95 degree Celsius rated wire. The specs for this chord goes up to 90 degrees "C"....Operating temperatures range from -40C to +90C (-40F to 194F).
The 8 gauge, 3 wire (8/3) conductors are rated at 250V, 50A.
NEMA 6-50 configuration.