All cells don't have a nucleus . generally nucleus is found only in living cells .
example could be human cheek cells, onion cells , plant leaf cells .
But it's not necessary that all cells are living or we say all cells don't have nucleus .
an awesome example could be sclerenchyma about which i read last year when i was in
sclerenchyma are dead cells , they got no nucleus . so their function is just to provide rigid support.