That of a humble worker taking in the Royal Society? (6)
I believe the answer is:
person
'that of a humble' is the definition.
I can't judge whether this definition defines the answer.
'worker taking in the royal society?' is the wordplay.
'worker' becomes 'peon' (peon is a kind of worker).
'taking in' is an insertion indicator.
'the royal society?' becomes 'rs'.
'peon' placed around 'rs' is 'PERSON'.
Can you help me to learn more?
(Other definitions for person that I've seen before include "Type" , "present appearing in this" , "character" , "Individual human being" , "he's the third" .)