This seems to be a trivia question, but I can't find a button to add a movie into my watch list, in that movie page. The only button I can find is in the recommendation box:I know that I can add a movie through my watch list page, but that's not what I'm looking for:
How to add a movie to my watchlist in IMDb, in the movie page?
imdb
If it is the new site of IMDB then the Add to watchlist icon is just in front of the movie title. See the image below: 