There's no spell for lucid dreaming, most of the lucid dreamers have natural ability to dream lucid but still you can develop that ability.
I've been researching and working on lucid dreaming for a while and recently I made a Post on lucid dreaming. If you wish to develop that ability, feel free to checkout my article Lucid Dreaming: A Doorway for beginners . You can find it on my history.
If you've any queries, feel free to ask, blessed be :-)