The recommended way is to use the absolutePath() function provided by jevois::Component (available in Module since Module inherits from Component):
http://jevois.org/doc/classjevois_1_1Component.html
In you case, use
cv::FileStorage fs(absolutePath("file.yaml"), cv::FileStorage::READ);
to get file.yaml from inside the module's path (/jevois/modules/Vendor/ModuleName/file.yaml)
You may also want to use some macros defined in Config.H of jevois. Please check out ~/jevois/include/jevois/Config.H.in
then two versions are created by CMake, one in hbuild/ and the other in pbuild/. Config.H is finally auto-included by every file that is compiled by our CMake scripts. So you can use any of the definitions in there, and their mappings will be correct for either host or platform. For example, JEVOIS_ROOT_PATH, JEVOIS_ENGINE_INITSCRIPT or JEVOIS_SHARE_PATH, etc