Here's why:
* daad means "deed" or "act" and is a thing, making it a noun.
* baie is an adverb meaning "very" or "many".
* dankie is an interjection expressing thanks.
* vir is a preposition.
* die is a definite article (like "the").
* goeie is an adjective describing the noun "daad".
* wat is a relative pronoun.
* jy is a pronoun.
* your is an adjective, but it's not grammatically correct in this sentence.
* gedoen is a verb.
* het is a verb.
Therefore, "daad" is the only word in the sentence that functions as a noun.