If reading the guide linearly, it makes sense to have the PKM chapter directly after Designing Bitcoin Products. This chapter details how various schemes work and which to choose. As someone designing a bitcoin application, deciding on what PK scheme to use is something decided prior to designing the internals (such as onboarding, which shows how to integrate your selected scheme) UI of the application.
If reading the guide linearly, it makes sense to have the PKM chapter directly after Designing Bitcoin Products. This chapter details how various schemes work and which to choose. As someone designing a bitcoin application, deciding on what PK scheme to use is something decided prior to designing the internals (such as onboarding, which shows how to integrate your selected scheme) UI of the application.