This repo: http://git.yoctoproject.org/cgit/cgit.cgi/patchtest-oe This tutorial may be helpful: https://github.com/david-a-wheeler/spdx-tutorial Also see this example: https://lists.yoctoproject.org/pipermail/yocto/2019-June/045552.html
patchtest-oe is now obsolete (tests have been moved to oe-core) and SPDX identifiers have been added there, so this can be closed.