Which way is the quickest to access the Find and Replace dialog box?

The quickest way I'd say is using the keyboard combination keys Ctrl + H

Explanation:

The Find and Replace feature in Word is used to quickly make revisions. This feature is best used when you have repeatedly made mistakes in your document or you need to exchange a particular word for another. This feature can also be used in other situations like when you need to search for a specific word or number. Holding down the Ctrl + H is the quickest way to fire this feature up.