Here is a list of Magento advanced interview questions that I can think off now.
EDIT: There are also Expert interview questions that I added lately.

1. Explain Magento’s MVC architecture
2. How Magento’s ORM work?
3. What is EAV in Magento?
4. Difference between Mage::getSingleton() and Mage::getModel()
5. What are the steps to change the theme of Magento
6. If you want to add/modify core functionality, how will you do it?
7. How will you create a new module in Magento?
8. How will you call a CMS page in your module’s PHTML file?
9. What is codePool in Magento?
10. Explain handles in Magento’s layout
11. What is in Magento’s config XML?
12. Explain Magento’s URL structure
13. How will you optimize Magento featured website?
14. Explain in detail cache management in Magento
15. When will you need to clear cache to see the changes in Magento?
16. Explain the flow of placing an order technically
17. How will you enable product’s custom attribute visibility in frontend?
18. How will you upgrade your custom module?
19. Difference between EAV and flat table
20. Is it mandatory to give Namespace while creating custom module in Magento?
21. How will you override Block/Model/controllers in Magento?
22. What is difference between override and rewrite?
23. How will you add/remove content from core’s system.xml file?
24. Can you have more than one Grid in a module?
25. How will you join flat table and EAV table in Magento?
26. How will you enable maintenance mode of your Magento website?
27. What are “magic methods” in Magento?
28. How many database tables will Magento create when you make a new EAV module?
29. Explain Magento’s Collections
30. Explain events and observers in Magento
31. Difference between block’s “name” and “as” attributes in layout XML
32. When to use session and when to use registry to store variables?
33. Where will you write your module’s business logic in Magento?
34. Explain different types of sessions in Magento (e.g. customer/session, checkout/session, core/session) and the reason why you store data in different session types.
35. What are the commonly used block types? What is the special in core/text_list block type.
36. What are the different design patterns used in Magento?
37. What can you do to optimize Magento performance?
38. Where is the relation between configurable product and it’s simple product stored in database?
39. How will you log current collection’s SQL query?
40. How to get first item or last item from the collection?

If you are looking for answers to these questions, check it out here:
Magento Interview questions and answers for experienced and freshers

Best luck!