From personal experience, what's initially associated with worker? (2,5,4)
I believe the answer is:
at first hand
'from personal experience' is the definition.
(from direct experience)
'initially associated with worker?' is the wordplay.
'initially' becomes 'at first' (synonyms).
'associated with' means one lot of letters go next to another.
'worker?' becomes 'hand' (hand is a kind of worker).
'atfirst'+'hand'='AT FIRST HAND'
'what's' acts as a link.
(Other definitions for at first hand that I've seen before include "Starting bridge tournament" , "From the original source" , "from personal experience" , "Directly" .)