hi i wanted to ask if i can stop and opponent from stealthing my chars with bowl of brown and what abilities can brienne of tarth ( the stark and baratheon one) cancel. tnx a lot!

No, Stealth is a keyword, not a triggered ability. In general, a triggered ability is one of the form " Action : Do stuff." where "Action" will be the word Response, Any Phase, or the name of a specific phase.

Also, Brienne doesn't cancel anything. It prevents your opponent from even attempting to trigger any effects (see the explanation of what those are above). This is not the same thing as cancelling an effect.