The Speaker’s dogged disquisition? (5)
I believe the answer is:
tract
'disquisition?' is the definition.
(thesaurus)
'the speaker's dogged' is the wordplay.
'the speaker's' indicates a 'sounds like' (homophone) clue.
'dogged' becomes 'tracked' ('track' can be a synonym of 'dog').
'tracked' sounds like 'TRACT'.
(Other definitions for tract that I've seen before include "Political pamphlet" , "Pamphlet, large expanse of land" , "Stretch of land or religious pamphlet" , "Publication" , "Part of body" .)