Demonstrated in what manner to cut tin (5)
I believe the answer is:
shown
'demonstrated' is the definition.
(I've seen this before)
'in what manner to cut tin' is the wordplay.
'in what manner' becomes 'how' (synonyms).
'to cut' indicates putting letters inside.
'tin' becomes 'Sn' (Sn is the chemical symbol for tin).
'how' placed within 'sn' is 'SHOWN'.
(Other definitions for shown that I've seen before include "Demonstrated" , "Displayed" , "Explained" , "Exhibited" .)