Sort of info lawyers know to begin with (3)
I believe the answer is:
ilk
'sort' is the definition.
(ilk can mean a type or kind)
'info lawyers know to begin with' is the wordplay.
'to begin with' indicates taking the first letters.
The first letters of 'info lawyers know' is 'ILK'.
'of' acts as a link.
(Other definitions for ilk that I've seen before include "Like" , "Type - kind" , "Type of milksop" , "Sort or type of silks" , "Kind, class" .)