"...fascinates me most..." seems to me preferable. The word "the" doesn't add any value. Also, you could rephrase the sentence as "Of all the things I've learned about the textile industry, I am most fascinated by the fact that it drives..." or Of all the things I've learned about the textile industry, most fascinating to me is the fact that it drives..." Both of these formulations, to my ear, do not call for "the" before "most". So I think it can well be omitted in the original sentence.