Due to my own background, I may be remembering more discussed on the topic than there actually is, but the translation on Marxism.org uses the phrase intellectual production multiple times to discuss what is clearly a form of intellectual property. The concept of The Commons, including it’s form as a well from which ideas are drawn, goes back thousands of years. And while it may not be an exact 1 to 1 of our present day, Marx was definitely familiar with the enclosure of The Commons. I doubt he would have that much of a problem extrapolating a scenario resembling our present day.