Research first of Protestant beliefs attributed to old partner (7)
I believe the answer is:
explore
'research' is the definition.
(I know that research can be written as explore)
'first of protestant beliefs attributed to old partner' is the wordplay.
'first of protestant' becomes 'p' (1st letter of 'protestant').
'beliefs' becomes 'lore' (lore can mean traditions or beliefs).
'attributed to' says to put letters next to each other.
'old partner' becomes 'ex' (an ex-partner).
'p'+'lore'='plore'
'plore' after 'ex' is 'EXPLORE'.
(Other definitions for explore that I've seen before include "Examine or investigate, new country or possibilities" , "Investigate in detail" , "Look around; examine" , "Travel in search of discovery" , "Examine by touch" .)