There are several synonyms that can be used in place of the phrase "dost off the top of your head." Some options include the phrases "spout off," "rattle off," "recite," or "utter without thought." These phrases all have a similar meaning, which typically refers to speaking without prior thought or consideration. In some cases, these phrases may also suggest speaking quickly or recklessly, without concern for potential consequences. Ultimately, the choice of synonym will depend on the context in which it is being used and the nuance or tone that the speaker wants to convey.