Little Edmund in food stores showing displays of useless knowledge (10)

'displays of useless knowledge' is the definition.
'pedantries' can be an answer for 'displays' (pedantry is a kind of display). I am unsure of the 'of useless knowledge' bit.

'little edmund in food stores' is the wordplay.
I cannot quite understand how this works, but
'edmund' could be 'ed' and 'ed' is found in the answer.
'food' could be 'e' (E is an example) and 'e' is found in the answer.
This explanation may well be incorrect...

'showing' is the link.

Can you help me to learn more?