You can find pretty much everything using DTK. Most of the sections are for searching specific categorized segments of the code, but the bottom-most field is for searching "everything". It does require that you specific PHP vs JS, but it searches all (known Zen Cart-related) directories.
You didn't specify:
a) what exactly you're searching for and why --- your screenshot doesn't really say what you're looking to find or change, so we can't give you any specific answers
b) what version of Zen Cart you're using --- without that we can only assume you're using the latest version, which has all the best features, but if you're using an older version then you might be getting wrong advice
c) what additional plugins you've got installed, and what other alterations have been made to the site --- because these change the normal operation and therefore change the answers to your questions
While some people such as @torvista don't use DTK, the DTK does give strong search capability for any store admin who doesn't keep a copy of the site files on their own PC.
But if you do keep a copy on your PC, then you've got additional tools at your disposal depending what software you possess. I've found that Sublime Text is a great text-editor (designed for software development), and has fantastic and fast search capability. They encourage you to buy a license, but their trial mode is timeless so no need to invest if you don't use it often.
(The DTK isn't for editing; it's just for searching, which is handy for diagnosing problems as well as demonstrating findings when asking for support, etc.)
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