Is this (the phrase/word ごとが) a grammar point or vocabulary? I tried to look it up in Takoboto dictionary but it doesn't return a specific word.
Also, if the phrase/word 「ごとが」 is a grammar point. How do I use it?
The context, where I found the word, lies in the song 翼をください (an ending song version of Nichijou)
I'm assuming you mean the ごとが in
いま私の願いごとがかなうならば翼がほしい
If this is the case, then you're parsing the sentence incorrectly. The ごと forms part of a noun phrase with 願い. You can find it on Takeboto under お願い事. Here's the underlying structure (I've used bold to highlight the different grammatical components):
願いごと が かなう
The が is your standard subject marker. Thus, the subject of the sentence is 願いごと and the main verb is かなう, which means for a 願い to be come true/be fulfilled.
Presumably you are referring to this part of the lyrics:
いま わたしの願いごとが
叶うならば 翼が欲しい
この 背中に鳥のように
白い翼 つけてください
In which case you are parsing it incorrectly. It actually breaks down like this
いま わたしの 願いごと が
Where 願いごと means "desire" or "thing wished for". In conjunction with the next line, it's saying "If my wish were fulfilled now..."
