Dodgy look, unknown quantity? That’ll make you cautious (5)
I believe the answer is:
leery
'cautious' is the definition.
(I've seen this in another clue)
'dodgy look unknown quantity?' is the wordplay.
I cannot quite understand how this works, but
'look' could be 'leer' (leer is a kind of look) and 'leer' is present in the answer.
'unknown' could be 'y' (algebra) and 'y' is found within the answer.
No letters remain.
This explanation may well be incorrect...
'that'll make you' acts as a link.
Can you help me to learn more?
(Other definitions for leery that I've seen before include "In slang, wary or suspicious - reely!" , "Cunning - wary" , "Sly, cunning" , "Cautious due to suspicions" , "Shy" .)