Suppose you heard me tailing donkey? (6)
I believe the answer is:
assume
'suppose' is the definition.
(assume can mean to suppose or expect)
'you heard me tailing donkey?' is the wordplay.
'you heard' becomes 'U' (homophone of 'you').
'tailing' says to put letters next to each other (to tail can mean to go after or follow).
'donkey?' becomes 'ass' (ass is a term for a donkey).
'u'+'me'='ume'
'ume' put after 'ass' is 'ASSUME'.
(Other definitions for assume that I've seen before include "Suppose; put on" , "Take as read" , "Take as true or take for granted" , "Take for granted or take upon oneself" , "Take (responsibility)" .)