Coolest thing about engineer (12)
I believe the answer is:
technologist
'engineer' is the definition.
('technologist' can be a synonym of 'engineer')
'coolest thing about' is the wordplay.
'about' indicates an anagram.
'coolest'+'thing'='coolestthing'
'coolestthing' is an anagram of 'TECHNOLOGIST'.
(Other definitions for technologist that I've seen before include "Applied scientist" , "One who applies scientific knowledge" .)