I dont have the Ang but near the very end of Guru Granth Sahib Ji it talks about why the Guruship was passed from one to the next and the purpose each incarnation represented.
That's not necessarily the case. If you have a strong Punjabi base, you read Punjabi literature in addition to Gurbani, you read Punjabi non-fiction like books and newspapers, watch Punjabi-language news and you listen to katha, I don't think you need to watch Punjabi movies.
However, if you do none of those things, then Punjabi movies are a good starting-off point.