I had the same need of filter notes by "kind", specifically to see only notes added as bookmarks using the web clipper tool.
In the Grammar page (included in previous answers) I found that by typing "source:web.clip" in the search field I got what I wanted.
There is also options for filter notes added by mail, etc..
source:[string] - matches notes that came from an application or data source that matches the argument string. Not all notes will have a "source" attribute. Standard source attributes queries include:
Matches notes that were clipped from a web page using an Evernote Web Clipper
Matches notes that were clipped from a local mail client
Matches notes that were delivered to the service via the email gateway.
Matches notes that were created on an iOS client of some form.
Matches notes that were created on an Android client of some form.
Matches notes that were created on a mobile client of some form.
Hope this help you. Have a nice day