Researching 9/11 helped me awaken in 2008 and first redpill that sparked it is this early presentation by mechanical engineer Jim Hoffman.

In 26 minutes, Jim systematically dismantles the excuses given by the government for collapse of three World Trade Center buildings and clearly proves that these buildings fell due to controlled demolition. Apologies for the quality, it's the only copy I could find.

Jim's website is the best one for in depth research into the subject. Some of the info on this site cannot be found anywhere else anymore. Most of the slides in the video can be found here.

The second video that is important for understanding 9/11 is "September 11 -- The New Pearl Harbor", a 5 hour documentary that covers almost everything about 9/11 from the conspiracy angle. It is packed with old footage, interviews, and evidence.

It was made by filmaker Massimo Mazzucco. His documentary "Cancer -The Forbidden Cures" is also worth a watch.

The third video that I think is important for understanding 9/11 is Mark Passio's presentation that approaches the subject from the occult angle.

A former Satanic priest turned whistleblower, Mark is the best occult researcher who exposes how the cabal thinks and operates. This video is part of a much longer presentation about occulted subjects. To know your enemy, I recommend these presentations:

De-Mystifying The Occult

De-Mystifying The Occult Part 2: Satanism & The Dark Occult

You can find more at his webpage