Which group would have been most likely to criticize the knights of labor?

It would likely be "skilled workers" who would have been most likely to criticize the Knights of Labor, since many skilled laborers and factory owners saw this Union as allowing for unfair bargaining power on behalf of the workers. 

the noble might have thought that the system was far because they had lot of things and riches and the serf would have thought that the feudal system was un fair because of the way they were treated.

what are you options