(For context, it's said by one character attacking another) The phrase is 「やってやんよ」I've read somewhere that やます can mean 'to do/go' (google says the translation is 'I'll do it' But could it be one of those untranslatable things?
やってやんよ is a contracted form of やってやるよ.
- やって: the te-form of やる meaning "to do"
- やる (やん): やる meaning "to give", but as a subsidiary verb, it means "to do something to show one's ability" or "to do something for someone's sake"
- よ: a sentence-end particle
So the nuance of やってやんよ is either (or both) of "I'll do this to prove my power" or "I'll do this for you if you want me to". Something like this is typically said after the speaker has been provoked by someone, but it depends on the previous context. It's not the kind of phrase that can always be translated correctly without context (whish is probably why Google ignored the てやる part). But it's always possible to translate it to a similar English sentence if you understand the implication.
By the way, やます means nothing to me.