East African knowledge certainly not heading north (6)
I believe the answer is:
kenyan
'east african' is the definition.
(I've seen this before)
'knowledge certainly not heading north' is the wordplay.
'knowledge' becomes 'ken' (ken is a kind of knowledge).
'certainly not' becomes 'nay' (archaic form of 'no').
'heading north' says the letters should be written backwards (in a down clue, letters travel north).
'nay' written backwards gives 'yan'.
'ken'+'yan'='KENYAN'
(Other definitions for kenyan that I've seen before include "Native of Nairobi, say" , "Person from Nairobi, say" , "From Mombasa, for example" , "Native of Nairobi, perhaps" , "Commonwealth citizen" .)