I've grown frustrated with the "pseudo" query search syntax from Inbox. This is a hack but it works great (for me), when I want to search in a particular section. Here's an example: Say I want to search within my snoozed reminders for the phrase "Validate Warranty":
- Shift m (to focus on the side bar)
- Go down to the "Snoozed" section
- Focus on the 1st item (Right arrow)
- Press the "End" key (that should force loading a lot if not all of your items)
- Use your "find in page" feature from your browser.
(Please notice that these instructions assume you have keyboard shortcuts enabled).
I know this is not ideal, but I feel like Inbox has been semi-abandoned by the Google folks; this is a hack.