Irritable single heartless canine emotes initially (2,4)
I believe the answer is:
on edge
'irritable' is the definition.
(I've seen this before)
'single heartless canine emotes initially' is the wordplay.
'single' becomes 'one' (similar in meaning).
'heartless canine' becomes 'dg' (I am not sure about this - if you are sure you should believe this answer much more).
'initially' suggests taking the first letters.
The initial letter of 'emotes' is 'e'.
'one'+'dg'+'e'='ON EDGE'
Can you help me to learn more?
(Other definitions for on edge that I've seen before include "Cliff-top walker may be" , "Nervous and tense - close to cliff?" , "Anxious, nervy" , "Fidgety, nervous" , "Apprehensive" .)