Put the pre-built validation layers into the folder for the architecture you're targeting.

E.g. for armeabi-v7a:

• ./armeabi-v7a/libVkLayer_core_validation.so
• ./armeabi-v7a/libVkLayer_object_tracker.so
• ...

After this, build the example you want validation to be enabled for with the "-validation" flag, e.g.:

build pbrtexture -validation