Can I Show "It's A Wonderful Life" ?

The copyright laws are quite complicated and often misinterpreted by lawyer and non-lawyers.

For years this film was considered Public Domain. However, NBC is the copyright holder for broadcast..

The film IT'S A WONDERFUL LIFE is not - REPEAT IS NOT  IN THE PUBLIC DOMAIN - and everyone in the biz recognizes that now. Even though many once believed that the film itself lost some copyright protection, and at some time, the market was flooded with broadcasts and videos, today it is accepted that the copyright holder of the original work still controls all film rights to the original work. Thus the film, a derivative work, cannot be sold, distributed, copied, broadcast without the consent of the copyright holder of the original work. For example, to date, only NBC has the broadcast rights and that's why you only see it on NBC.  And anyone, who shows the film to the public or otherwise distributes, etc.. without the consent of the copyright holder of the original work, is subject to civil (statutory damages and legal fees runs into the tens and tens of thousands) and perhaps criminal liability for copyright infringement.