Drunken sot, I see, showing no emotion (5)
I believe the answer is:
'showing no emotion' is the definition.
(I've seen this in another clue)
'drunken sot i see' is the wordplay.
'drunken' indicates an anagram.
'see' becomes 'C' (the word for the letter, according to Chambers).
'sot' with letters rearranged gives 'sto'.
(Other definitions for stoic that I've seen before include "Uncomplaining in suffering" , "Long-suffering type; follower of Zeno" , "Greek in school" , "the original Zeno?" , "Someone seemingly indifferent to pleasure or pain" .)