Hi, a good tool is "locate". It will find the listing in the file-database.
To be sure it (file-database) is up to date, type
Them use locate to find the file...
The is probably in /usr/bin/ or /usr/local/bin/ (/usr/bin/digikam)
Another thing that could happen is when you upgrade a program and the link (shotcut) still points to the old file.
if updatedb does not work (usually fine) "symlinks" and "ldconfig" can repair this most of the time.
Look up the help pages for those apps.
HTH, Glenn