The JUNOS COS architecture is the same for all JUNOS products, slight differences exist in the number of supported queues per interface/card, and ability to deliver granular scheduling/shaping per queue/subinterface/phys.interface.
This Day1 book has it explained https://www.juniper.net/documentation/en_US/day-one-books/DO_Deploying_Basic_QoS_v2.zip
If You are familiar with CSCO IOS COS then this whitepaper can be useful
If You want to read about per-platform peculiarities then "Juniper MX series" book has a big chapter on MX COS.
I am not aware of EX-specific and SRX-specific COS books, You may need to read the tech docs for these platforms but good news is that MX has most comprehensive COS and EX/SRX COS is subset of MX COS.
If all fails and You are still stuck, call Your Juniper Account team to ask for Juniper Prof.Services help! 😀