Which libraries are available to link in cmake?

Question

I was learning CMake for a project and feel confused when linking libraries.

I find it easier to ask with an example, as using terms I am not familiar could be misleading.

The questions are (also commented in the example codes)

1. how can I know what are the library name I can link to my target? Can I tell that from the build file structure, or I need to look into CMakeLists.txt of the external libraries. (e.g. the gtest-main and libhermes in the example)
2. How can I use a "grandchild" library that is part of the external library? (e.g. the jsi library in the example)

Example

Let's say I am writing some tests with dependency on the Hermes Library. I then write a CMakeList.txt file like

cmake_minimum_required(VERSION 3.13)
project(mytests_cxx)

set(CMAKE_CXX_STANDARD 14)

include(FetchContent)

FetchContent_Declare(
  hermes
  URL https://github.com/facebook/hermes/archive/d63feeb46d26fe0ca7e789fc793f409e5158b27f.zip
)
FetchContent_MakeAvailable(hermes)

enable_testing()

add_executable(
  hello_test
  ./test.cpp
)

find_library (
  LIB_HERMES
  hermes # <- how can I know what is the name?
)


find_library (
  LIB_JSI
  jsi # <- How could I use a "grandchild" dependency, it is defined here (https://github.com/facebook/hermes/tree/main/API/jsi/jsi)
)

target_link_libraries(
  hello_test
  gtest_main <- Hermes seems to use gtest, how could make sure gtest_main is available?
  LIB_HERMES
  LIB_JSI
)

include(GoogleTest)
gtest_discover_tests(hello_test)

Running cmake to build

cmake -S . -B build -DHERMES_BUILD_SHARED_JSI=ON // I see an option defined in heremes'CMakeLists.txt but not sure if I am using it right.

the directory in build

tree ./build -L 2
./build
├── CMakeCache.txt
├── CMakeFiles
│   ├── 3.23.1
│   ├── CMakeDirectoryInformation.cmake
│   ├── CMakeError.log
│   ├── CMakeOutput.log
│   ├── CMakeRuleHashes.txt
│   ├── CMakeTmp
│   ├── Makefile.cmake
│   ├── Makefile2
│   ├── Progress
│   ├── TargetDirectories.txt
│   ├── cmake.check_cache
│   ├── hello_test.dir
│   └── progress.marks
├── CTestTestfile.cmake
├── ImportHermesc.cmake
├── Makefile
├── _deps
│   ├── hermes-build
│   ├── hermes-src
│   └── hermes-subbuild
├── bin
│   └── hermes-lit
├── cmake_install.cmake
├── compile_commands.json
└── hello_test[1]_include.cmake

then I run cmake --build build and see this error

/.../test.cpp:8:10: fatal error: 'jsi/jsi.h' file not found
#include <jsi/jsi.h>