CANopen frame format?
Generally I've found that actual device manuals usually have the easiest to understand descriptions of the CANopen protocol. They are hands on, and seem to have a much more practical approach than many other materials. 

For example this one I found quite easy to follow:
http://www.a-m-c.com/download/sw/dw300_3-0-3/CAN_Manual300_3-0-3.pdf

Over at stackoverflow other people have asked similar questions and they've gotten a good amount of answers:
https://stackoverflow.com/questions/1232624/how-to-program-a-simple-canopen-layer