If you use dh_apport ("dh --with apport") from the dh-apport package, put the hook into debian/libmirserver0.apport (in general: debian/<binarypkgname>.apport) if it should only apply to the libmirserver0 library package, or debian/source.apport if it should apply to all binary packages from the source package.
If you install them without dh-apport: Put them into /usr/share/apport/package-hooks/source-mir.py (i. e. source-<srcpkgname>.py) to apply to all binaries, or into /usr/share/apport/package-hooks/libmirserver0.py (i. e. <binarypkgname>.py) to only apply to a specific binary.
If you use dh_apport ("dh --with apport") from the dh-apport package, put the hook into debian/ libmirserver0. apport (in general: debian/ <binarypkgname> .apport) if it should only apply to the libmirserver0 library package, or debian/ source. apport if it should apply to all binary packages from the source package.
If you install them without dh-apport: Put them into /usr/share/ apport/ package- hooks/source- mir.py (i. e. source- <srcpkgname> .py) to apply to all binaries, or into /usr/share/ apport/ package- hooks/libmirser ver0.py (i. e. <binarypkgname>.py) to only apply to a specific binary.