Signal Princeton educator to include it, on reflection (6)
I believe the answer is:
denote
'signal' is the definition.
(I've seen this in another clue)
'princeton educator to include it on reflection' is the wordplay.
'princeton educator' becomes 'eed' (I can't justify this - if you can you should give a lot more credence to this answer).
'to include' is an insertion indicator.
'it' becomes ''t' (abbreviation. e.g. in 'tis).
'reflection' says the letters should be written backwards.
't'+'on'='ton'
'eed' placed around 'ton' is 'etoned'.
'etoned' written backwards gives 'DENOTE'.
Can you help me to learn more?
(Other definitions for denote that I've seen before include "Point" , "Stand as symbol for" , "Need to (anag) - indicate" , "Mean or signify" , "show" .)