Occupation of attendant conserving energy (6)
I believe the answer is:
career
'occupation' is the definition.
(career is a kind of occupation)
'attendant conserving energy' is the wordplay.
'attendant' becomes 'carer'.
'conserving' means one lot of letters goes inside another.
'energy' becomes 'e' (physics symbol as in E=mc2).
'carer' placed around 'e' is 'CAREER'.
'of' is the link.
(Other definitions for career that I've seen before include "making progress" , "Quick" , "Vocation; rush" , "Rush headlong" , "Life (in terms of work etc)" .)