Duty (and where it often lies) (4)
I believe the answer is:
onus
'duty' is the definition.
(I've seen this before)
'and where it often lies?' is the wordplay.
I cannot really understand how this works, but
'and' could be 'n' (common abbreviation for 'and') and 'n' is located in the answer.
The remaining letters 'ous' is a valid word which might be clued in a way I don't see.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for onus that I've seen before include "'Burden, load (4)'" , "Duty or responsibility" , "'Responsibility, task or burden (4)'" , "'Burden, of proof (4)'" , "Burden, duty" .)