2 questions:

1), Can i put a character with ambus if Brienne the tar is in the challenge? i know that a keyword cant be cancelled, but i understand that ambus is Any phase: put a character...bla bla ba.

2) Can I activate Naval enhanc. with Brienne in the challenge?

Thanks.

First, she is Brienne of Tarth.

1) Brienne doesn't cancel anything. Ambush is a triggered effect (Any Phase: bla bla bla), so you can't use it while an opponent's Brienne is in the challenge.

2) Declaring a naval attacker or defender is not a triggered effect, it's a game mechanic. So Brienne does not prevent it.

Is Ambush definately a triggered effect?

I thought it was a keyword as per Deadly, Renown, Intimidate and therefore not triggered

Otherwise, does this mean that Brienne can defend against a deadly attack and not have to worry about deadly being triggered? ... or oponents could not clain for renown (definely passives, surely)

Some keywords are triggered (Ambush), some act as passives (deadly), some have their own framework (renown), others as conditional constants (Intimidate).

Being a keyword doesn't unify their timing, it just means that uniformly a) they can be affected by gain/loses keywords, b) they cannot be cancelled, c) they can affect characters immune to character abilities... (etc).

As neither Deadly nor Renown is triggered, Brienne has no interaction with them whatsoever.

Is Ambush definately a triggered effect?

I thought it was a keyword as per Deadly, Renown, Intimidate and therefore not triggered

Otherwise, does this mean that Brienne can defend against a deadly attack and not have to worry about deadly being triggered? ... or oponents could not clain for renown (definely passives, surely)

Passives trigger themselves (or the game does). Basically a non-player identity is triggering those effects. Brienne explicitly affects effects that the player has direct control of whether or not they are triggered.

I hate putting affect and effect next to each other... It looks so stupid...