An event Jews won't forget or ignore (8)
I believe the answer is:
passover
'won't forget or ignore' is the definition.
I can't tell whether this definition defines the answer.
'an event jews' is the wordplay.
'an event' becomes 'pass' (pass is a kind of event).
'jews' becomes 'over' (I can't justify this - if you can you should give a lot more credence to this answer).
'pass'+'over'='PASSOVER'
Can you help me to learn more?
(Other definitions for passover that I've seen before include "feast - with 25a" , "spring festival" , "religious festival" , "Disregard - Jewish festival" .)