You can use the get_property command to retrieve the value of the directory property
INCLUDE_DIRECTORIES
Something like this:
get_property(dirs DIRECTORY ${CMAKE_CURRENT_SOURCE_DIR} PROPERTY INCLUDE_DIRECTORIES)
foreach(dir ${dirs})
message(STATUS "dir="${dir}"")
endforeach()
The value of this directory property only tracks the include_directories commands that have occurred previously in the same CMakeLists file, or that have been inherited from previous occurrences in a parent CMakeLists file. If your find_package and include_directories commands are scattered about throughout many subdirectories, this becomes a challenging issue.
If you get to that point, you may consider overriding the include_directories command with your own function or macro and track the values passed to it yourself. Or, simply accumulate them in a global property or an internal cache variable alongside each call to include_directories.
See the documentation here:
https://cmake.org/cmake/help/latest/command/get_property.html
https://cmake.org/cmake/help/latest/prop_dir/INCLUDE_DIRECTORIES.html