I forgot to mention that Venser, the Sojourner's abilities can only be activated at sorcery speed (only on your main phases). Therefore you can't even exile the angel token during the combat phase anyway, since it is only created and placed onto the battlefield during the combat phase.
I don't quite get the question, so do correct me if I am mistaken in my reply.
If you were to declare Geist of Saint Traft as an attacker and exile it through a card like Restoration Angel, the angel token will still be placed onto the battlefield due to Geist of Saint Traft's ability. However the angel token will still get exiled at the end of combat, whether or not Geist of Saint Traft was exiled. Triggered abilities will still be placed onto the stack and resolve regardless of what happens to their source.
A note though, you will not be able to exile Geist of Saint Traft in combat with Venser, the Sojourner's plus ability since you can only activate it at sorcery speed. That means you can only exile Geist of Saint Traft before or after combat, to which the angel token will not be created or will be exiled respectively.
Abilities and spells are two very different things.
Abilities can be static, triggered or activated. They can't be casted and can only be found on permanents. In this example, Venser, the Sojourner is a permanent with 3 activated abilities which you can only use one of it once per turn at sorcery speed.
Spells are generally casted from hand, though there are some cards which let you cast from the library and graveyard (but we won't go into that in depth yet). There are different types of spells - Permanent spells, Instants and Sorceries.
I don't mean to be rude and unfriendly, but I do suggest reading up and understanding your basic Magic rules first (link here). If there remains any doubts, do feel free to continue asking.
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