You can search for pages with Talk discussions using the Confluence Search:

Confluence Search field in the header

Use the standard Confluence Search field in the header to enter your query. 

The search queries syntax is the following:

QuerySearchExamples
macroName:talk
Find all Confluence pages with at least one Talk macro 
talk:"some text"By text in discussions

talk:release

talk:"do that ASAP"

talkUser:"User Name"By commenter (by user name, first name, last name or full name)

talkUser:asmith

talkUser:Alex

talkUser:Smith

talkUser:"Alex Smith"

talkUpdated:[yyyymmdd TO yyyymmdd]By talk update date rangetalkUpdated:[20141201 TO 20150201]
macroName:talkFor Talk macromacroName:talk

talk:"some text" AND talkUpdated:[yyyymmdd TO yyyymmdd] 

talk:"text 1" OR talk:"text 2"

talkUser:"User Name 1" NOT talkUser:"User Name 2" 

(variations are possible)

By several terms

talk:"do that ASAP" AND talkUpdated:[20141201 TO 20150201]

talk:change OR talk:modify

talkUser:asmith NOT talkUser:jclarks

Make sure to include your query in double quotes if it contains spaces.

The Confluence Search Syntax, you can: