opponent moves kennen from base to open battlefield in response I thrill of the hunt my nidale from the other battlefield open who is the attacker and defender? and if that was not legal I guess I needed to wait until my focus to cast thrill of the hunt? then who is attacker defender still?

Opponent is the Attacker, you're the Defender — and yes, your Thrill of the Hunt was a legal play.

Thrill of the Hunt has [Reaction], so it's playable in the Closed state the opponent's move created, and it doesn't change who applied Contested. The opponent moving Kennen to an empty battlefield applied Contested first, which locks them in as Attacker (Rule 464.2.c.1); your Nidalee arriving afterward — by any means — makes you the Defender. When the non-combat showdown continues and becomes a Combat Showdown (enemy units now present), the designations don't flip.

Waiting for your Focus wouldn't have changed anything either — the Attacker/Defender split is decided by who first contested the battlefield, not by who acts first or when you join. Note Nidalee only gains the Defender designation, so no attack triggers for you, but Cat Form's "when I win a combat, draw 1" still works since she's in that combat.