Resources
Finding historical X and Motif documentation
Using (mostly) archived material
Because Motif is over thirty years old, a lot of the information which was on the Internet at that time has resided on old university servers long since vanished.
Kenton Lee, who was an X11/Motif freelance programmer had a brilliant site of Motif resources.
The Kenton Lee collection
Kenton Lee's Site (mirrored), is a useful starting point for exploring tutorials, papers and software from the X and Motif community. Follow its X-related sites directory to discover material by topic.
It is a historical collection.