It doesn't matter if it's dis or dat duck? (5)
I believe the answer is:
eider
'duck?' is the definition.
(eider is a type of duck)
'it doesn't matter if it's dis or dat' is the wordplay.
I cannot really understand how this works, but
'it' could be 'e' ('e' can mean 'electronic' which is similar to 'IT') and 'e' is found within the answer.
'matter' could be 'er' (Er is an example) and 'er' is present in the answer.
The remaining letters 'id' 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 eider that I've seen before include "Large sea duck" , "Species of duck" , "Reed I turn into a duck" , "Duck with soft feathers" , "Duck from which down is obtained" .)