The following sentence misuses the word accept: "I'll take all the cupcakes accept the one with cream cheese icing." Which part of language involves knowing the proper use of the word accept?

Lexicon.

Explanation:

Lexicon is demonstrated as the element of language that includes the vocabulary or words involved in a particular language that assists in its meaningful formation. It is the element of the language that proposes an opportunity to form varied combinations of words for forming various sentences into a reasonable structure.

In the given sentence, the 'lexicon' part of the language would involve the proper use of the word 'accept' as it describes the appropriate use of the word into a meaningful (lexical) and logical framework or sentences. As per the 'lexicon', the appropriate word here would be 'except' as per the context of the sentence. Therefore, the 'lexicon' is the answer.