Sound knowhow, but substandard English (5)
I believe the answer is:
nohow
'sound knowhow but substandard english' is the definition.
I can't judge whether this definition defines the answer.
'sound knowhow' is the wordplay.
'sound' indicates a 'sounds like' (homophone) clue.
'knowhow' sounds like 'NOHOW'.
Can you help me to learn more?
(Other definitions for nohow that I've seen before include "Under no circumstances (as Tweedledum said)" , "Definitely not" , "Not at all in US" , "Absolutely not in America" , "Not in any way (colloq.)" .)