Critically examines about nearly all the manservants (6)
I believe the answer is:
valets
'the manservants' is the definition.
(valet is a kind of manservant)
'critically examines about nearly all' is the wordplay.
'critically examines' becomes 'vets' (I've seen this before).
'about' means one lot of letters goes inside another.
'nearly all' becomes 'al'.
'vets' going around 'al' is 'VALETS'.
(Other definitions for valets that I've seen before include "Gentlemen's gentlemen" , "Manservants" .)