The correct answer is "This"
Step-by-step explanation:
In grammar, a demonstrative pronoun refers to a word that is used to point out or show specific ideas, objects, places, entities, etc. In the English language, there are only four demonstrative pronouns, these are this, that, these and those. Additionally, each of these pronouns is used in different cases, for example, this and that can only be used for singular nouns and they refer to near objects or entities.
This implies in the sentence "This is not the right time to bring it up" the demonstrative pronoun is the word "this" because this word is used to point a specific entity "the right time" and also is one of the four existing pronouns in the English language.