The phrase "dost off top your head" is an old English expression that means to think of something quickly and without much thought or research. There are many synonyms that can be used instead of this phrase, depending on the context. Some of the common synonyms include "recollect," "recall," "remember," "remind," "retrieve," "think of," "call to mind," and "summon up." Each of these synonyms has a slightly different shade of meaning, so it's important to choose the one that best fits the specific situation. When looking for a replacement for this phrase, it's important to consider the tone, register, and style of your writing or speech.