Where do I pick up from after finishing the Deltora Quest anime?
The first 8 books were adapted into a 52+13 episode series by OLM.

Please note that the 13 episodes after the 52 episodes are original and not part of the original novels.

The Deltora Shadowlands (3 books) and Dragons of Deltora (4 books) series are where you can continue from. Depending on your location, you may order them from online book distributors (in physical or e-book format) or see if they are available in your local library in electronic format.