How do I browse for available gsettings options?

You could also do that in CLI with gsettings:

gsettings range SCHEMA [:PATH]  KEY

where

range
           Queries the range of valid values for KEY.

In your case:

$ gsettings range org.freedesktop.Tracker.Store verbosity
enum
'errors'
'minimal'
'detailed'
'debug'

The newer version of dconf-editor now lists the options.

enter image description here

In this example, if you click on debug, you'll see a list of other available values. This screenshot is of version 0.10 of the tool.

A screenshoot from v0.19.3, shows options:

enter image description here

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