If Kennen moves to a battlefield then gets gusted will the stunns till go off

Yes — the stun still resolves. Kennen's trigger reads "When you play me or I attack, you may pay [2] to [Stun] a unit" — no "here," so it doesn't reference his location. Once the trigger is on the Chain with the [2] paid and the target chosen at finalization, Gust returning Kennen to hand doesn't affect it; the stun resolves normally (Rule 359.3.f.2 is what would break it, and Kennen has no such referent — contrast Vi, Peacekeeper).

The one thing that has to be true is that he actually attacked: "attack" triggers only fire when a unit gains the Attacker designation during Combat (Rule 383.4.e). Moving to an empty battlefield is just a Non-Combat Showdown, so no trigger and no stun.

Also worth knowing: Gust can only hit a unit with 3 might or less, so if Kennen is already at 4 might from his "+2 while there's a stunned enemy unit here," Gust can't even target him. And if it was Kennen revealed from Hidden, that play trigger is locked to "stun a unit here" and does fizzle when he's bounced (FAQ #12729) — the attack trigger is the one that survives.