Did more people see the 8 Harry Potter movies or read the 7 Harry Potter books?

This is difficult to calculate, because several people could have read one copy of the book. Also, people could have (almost certainly did) see any or all of the films more than once, so box office figures alone are a difficult way to calculate how many people saw the film. The films are also on DVD and have been shown on broadcast television, so it is almost impossible to calculate how many people may have seen them. You could do rough comparisons of book sales vs box office for the films, but it is unlikely there is a definitive answer for your question.

Plus both types of media can be shared and read or watched by many. Especially since libraries have copies of both available. Impossible to calculate.

The Harry Potter series of books has sold 450 million, best selling book series ever.
https://en.wikipedia.org/wiki/Harry_Potter#Films

The Harry Potter film series of eight films has taken 7.7 billion at the box office. Most successful film series ever,

https://en.wikipedia.org/wiki/Harry_Potter_(film_series)