In the URL! :)

https://www.themoviedb.org/movie/XXXX-this-is-the-movie-title.

Copy the number in the URL as XXXX.

For TV shows, you should use the TVDb ID.

Still having trouble. I watched the movie Clinical; can you walk me though how to find the TMDB ID? I am trying to add it to my Trakt TV movie list. Thank you

The movie is already on Trakt: https://trakt.tv/movies/clinical-2017

You can either Check in (i.e. scrobbling, you're watching it right now), or add it to your history (you've watching it in the past, you even add the specific day and time).

I watched the movie on Netflix and I wanted to add it to my watched list on Trakt, so how do I do that?

......

The movie is already on Trakt: https://trakt.tv/movies/clinical-2017

You can either Check in (i.e. scrobbling, you're watching it right now), or add it to your history (you've watching it in the past, you even add the specific day and time).

You can ask questions about Trakt here, this is TMDb:
http://support.trakt.tv

When I tried to add it to my watched list, it asked for the TMBD ID. It looks like it's a five digit number, but I can't find it on TMDB.

Then you're hitting the wrong button (probably import movie down below).

Please ask questions on Trakt.tv if you have problems using their site.