A major part of the DAT organic chemistry section is knowing your reactions. I have constructed the following reaction sheet to expose you to every reaction that could possibly show up on the DAT.
You do not need to memorize every single reaction to score well on the organic chemistry section. However, you should be familiar with trends such as nucleophilic addition to an electrophile, electrophilic aromatic substitution, substitution, and elimination, etc. Recognize that a certain functional group is required for a certain reagent to work. While there are hundreds of organic chemistry reactions, many of them work in similar fashion and use the same mechanism. By practicing and recognizing trends, you will be well on your way to crushing this section.