Hi m abdullah javed! How's it going?
I see from your profile that you hail from India. This 'knowledge is power' thing is just a 'saying'---an amusing, comforting little formulation of words. Its kind of one of the many verbal equivalents of 'good luck' charms, or 'bumper sticker' kind of things.
I recommend that you do not take it seriously. It is just an abstraction. There is one very important thing to remember, whatever language you are dealing with: Just because people open their mouths and talk and take pen to paper to produce words, it does not mean that those words always mean something. Sometimes people just push words around, looking for something to say.
Who knows what the provenance of the saying might be. Perhaps it was coined by an early blackmailer, for whom 'knowledge' (but strictly speaking, he would have been talking about 'information;' and there is a difference between 'knowledge' and 'information') would have indeed meant 'power' (but really he would have been talking about money; the 'information' would have given the blackmailer the 'power' to compel his target to pay him money, in order to prevent said blackmailer from revealing his victim's secret, whatever it might be).
Anyway, I think it is a situational thing people roll out for specific occasions. I do not think that the saying should be taken for a constant, ongoing injunction 'to live by.'