If I understand you aright, she is not using knowledge(s) to mean knowledge or knowledges , but to mean knowledges only. It that is the case, then in spite of what Barth has done, I highly recommend that she abandon it in favour of simply knowledges . (1) Such specialized formations are permissible in academic works, (2) her use is contrary to the accepted use of the parenthetical plural, and (3) it causes the ongoing concord problem that you have asked about.
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