Most High to examine everyone within (7)
I believe the answer is:
tallest
'most high' is the definition.
('tall' can be similar in meaning to 'high')
'examine everyone within' is the wordplay.
'examine' becomes 'test' (testing is a kind of examining).
'everyone' becomes 'all' (I've seen this before).
'within' means one lot of letters goes inside another.
'test' going around 'all' is 'TALLEST'.
'to' is the link.
(Other definitions for tallest that I've seen before include "Sell tat (anag.)" , "highest standing" , "most unlikely" , "Of greatest vertical extent" , "Top out" .)