You can search for your 2Dos in multiple areas within Purple Mash.
On the Home screen you can click on the 2Dos tab.
This will provide you with a list of 2dos you have set as well as a search bar. If you have tagged your 2Dos, you can also the search bar to search for 2Dos with a specific tag such as 'Reading' (as below).
You can also search for your 2Dos within your Work folders.