What philosophers have argued that "knowledge is power"? What sort of arguments did they put forward?
Michel Foucault was one prominent philosophy who emphasized the inseparability of knowledge and power. On Foucault's account, power is based on knowledge, makes use of knowledge, and reproduces knowledge. As a consequence, knowledge can never be neutral. For example, Foucault showed that epistemic claims about 'what counts as madness' have long been used to control the poor, the sick, and the homeless.
Scientia est Potentia.
Knowledge is power. Attributed to Francis Bacon, but I am relatively certain that it found expression amongst classical Roman authors, but I can't find the reference that I had anymore.
Foucault's arguments were slightly different, more complex, stating that all expression is political, and working to the power that cultural expression, which includes knowledge, can have. At least I think so, it has been a long time since I last read about him, and haven't read the original.