See, this is complex knowledge that helps to earn money - public material is available for the underlying technology (networking, advanced routing, TP) and the book by @Timothy_Hall adds to the official material.
The key is: Most people do the class after some first experiences with CP as they can ask questions and these get answered 😉 Apart from the lab exercises, all information (much more!) can be found in the Admin Guides:
CP_R81.10_Quantum_SecurityGateway_AdminGuide
CP_R81.10_Quantum_SecurityManagement_AdminGuide
CP_R81.10_SitetoSiteVPN_AdminGuide
CP_R81.10_RemoteAccessVPN_AdminGuide
CP_R81.10_MobileAccess_AdminGuide
CP_R81.10_IdentityAwareness_AdminGuide
CP_R81.10_ThreatPrevention_AdminGuide
CP_R81.10_Gaia_AdminGuide
...and many more are downloadable for free in UC !
CCSP - CCSE / CCTE / CTPS / CCME / CCSM Elite / SMB Specialist