WHICH will only tell you what YOU have set for your path. If your path isn't set correctly, it won't find anything. As already stated, start with running "locate strings", and if that doesn't work (as could very well be the case, because they probably are not running the "updatedb" command), you should next try "find / -name strings -print"... That command WILL take a while. Now I personally have "strings" located under "/usr/bin/", but I could just as easily had it under "/data/my_data/personal_stuff/bin/strings", or "/home/username/bin/strings", or "/opt/GNU/bin/strings", or basically anywhere the sys admin placed the software or mounted it from a remote system, or you yourself compiled, built, and installed....
If you use Red Hat or similar RPM based system, you can try running "rpm -qa | grep binutils" (at least on Red Hat, strings is part of the binutils RPM), and then you will know if it was installed. If this is a school system, it is also very possible that the system admin didn't install it on all the machines, and you might need to ssh into a different computer to access it....
EDIT:
Just saw you use SuSE which is RPM based, and the strings command is included in the binutils rpm. So you probably need to install the binutils rpm, which should be located on your installation DVD somewhere. Once you find the RPM file, do "rpm -ivh your_binutils_file_rpm_name"