Every time you eat cotton candy, you are reminded of the time you went to a carnival with your best friend and ate cotton candy until you were sick. in this scenario, the cotton candy represents:

 Retrieval cue

Explanation:

Retrieval cue is type of prompt that occurs in memory to recall any event .This reminder is caused due to any event or act happening presently that is similar to past event. In this case mind is triggered to access that event's memory and recall it.

According to the situation described in question, whenever cotton candy is eaten by an individual ,it reminds him/her about the past event of eating cotton candy in carnival and falling sick after that.

Thus, the situation is mentioning about retrieval cue.