Working range, where pan's filled with stew, originally (5,3)

'working range' is the definition.
(range of one's skills)

'pan's filled with stew originally' is the wordplay.
'pan' becomes 'skillet' (skillet is a kind of pan).
'filled with' is an insertion indicator.
'originally' suggests taking the first letters.
The first letter of 'stew' is 's'.
'skillet' placed around 's' is 'SKILL SET'.

'where' acts as a link.