/usr/include/GNUstep/StepTalk is in libsteptalk-dev 0.10.0-6+b3.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/include/GNUstep/../../lib/GNUstep/Frameworks/StepTalk.framework/Headers
/usr/include/GNUstep/../../lib/GNUstep/Frameworks/StepTalk.framework/Headers