Nordic question: Miss timing?

Yes, I used the search function and googled.

Tanngnjostr is a mandatory effect that when destroyed by battle and sent to GY, SS 2 nordic beast tokens.

Tanngnjostr is, when a monster you control is destroyed by battle and sent to GY, you can special summon this card.

Green Baboon is, when a beast-type you control is destroyed and sent to GY, pay 1000 to SS from hand or GY.

Given that tanngnjostr is mandatory SS 2 tokens, would the last thing happening be the tokens summoning themselves, or is this a SEGOC situation, and im able to SS tangnjostr/green baboon when tanngrisnir gets killed?

No, the last thing to happen would be Tanngrisnir being destroyed. It's effect would activate, then you are able to chain any Trigger effects with the same trigger, in this case Green Babboon or Tangjostr.

Mirror B is correct, you can chain Tangnjost effect to Tingrisnir effect after Tingrisnir has be destroyed by battle. However you can't activate Green Baboon effect since Green Baboon can't be activated in damage step.

Can you explain why tangnjostr works but baboon doesnt?

The official rulings for Green Baboon say that Green Baboon's effect cannot be activated in Damage Step.

generally, any optional trigger effect that is able to summon itself from the hand can't be activated in the damage step.