Does that particular book have an actual cover thumbnail image displayed on Kindle's homescreen or is it using a generic image that Kindle uses when the thumbnail image is missing?
If it is showing you a generic, "placeholder" image then the thumbnail file is missing (thus can't be found using search) and you would need to add an image with a correct filename. The filename "template" looks like this:
thumbnail_
ASIN_EBOK_portrait.jpeg
As for Java & MobiMetaEditor: all you need to to is
download install Java JRE (if your computer doesn't already have it installed) and then just open / double-click on MobiMetaEditor ".jar" file and it should open the UI window where you proceed to select the mobi or azw3 file for which you want to read the metadata, and then look at ASIN.