When your opponent activates a Normal Trap Card in response to your monster's attack declaration targeting an opponent's monster: You can discard this card; negate the activation, and if you do, destroy that card (this is a Quick Effect).
Can negate opponent’s Normal Trap cards during your Battle Phase
Must target your opponent’s monster for attack, as part of the activation condition.
Cannot be used outside Battle Phase.
Mirror Wall is a continuous Trap card, therefore it is not negated.
Treacherous Trap Hole and Paleozoic Canadia can be negated if they are activated in response to your monster’s attack declaration. However, if they were activated beforehand, you may not negate them with Chow Chow Chan.
The fact that you may not activate this card when you are doing a Direct Attack reduces this card’s flexibility, not to mention it is useless against Spells and Monster Effects.
These are some of the most prominently used protection cards that can only be activated when a monster declares attack. In this case, if and only if you were targeting your opponent’s monster in your attack, and these cards were activated, you can negate them with Chow Chow Chan. If it was a direct attack from you, you may not use Chow Chow Chan to negate these cards.
Negates the activation of your opponent's Trap Cards / Destroys your opponent's Trap Cards / Prevents responding to its activation
The effect seems to work only when the trap is activated in response to your attack declaration, but some traps like WoD can be activated after that during the Damage Step no? That really limits this card's usefulness