As a senior C# engineer, you have likely been through your fair share of interviews. However, if you’re on the other side of the table now and looking to hire someone for a C# engineering position, you want to make sure you’re asking the right questions to find the right candidate. Here are the top 10 interview questions for a senior C# engineer:

1. Can you walk me through your experience with C# and .NET Framework? This is a general question to understand the candidate’s experience with C# and .NET framework, and if they have been working with it for a while, they should be able to provide an overview of their experience with it.
2. Can you explain the difference between abstract classes and interfaces in C#? This is a fundamental question in C# programming, and a candidate who knows the difference can effectively design and develop applications using these concepts.
3. How do you handle errors in C#? Error handling is an essential part of software development, and a senior C# engineer should have a solid understanding of the various error-handling techniques in C# programming.
4. Can you explain the difference between value types and reference types in C#? Value types and reference types have a significant impact on how C# programs work, and an experienced C# engineer should know the difference and the implications of using each type.
5. Can you walk me through your experience with ASP.NET? ASP.NET is a critical web application framework in the .NET stack, and a senior C# engineer should have experience with it.
6. How do you approach testing in C#? Testing is an integral part of software development, and a senior C# engineer should have experience with testing frameworks like NUnit, xUnit, or MSTest.
7. How do you optimize the performance of C# applications? Optimizing the performance of C# applications is a crucial part of software development, and a senior C# engineer should know the best practices for optimization.
8. Can you explain the SOLID principles in C# programming? The SOLID principles are essential principles in object-oriented programming, and a senior C# engineer should be able to explain how they apply to C# programming.
9. Have you worked with any other programming languages other than C#? While C# might be a senior engineer’s primary programming language, they may have experience with other programming languages, which could be an advantage in certain situations.
10. Can you give an example of a complex project you have worked on in C#? This question aims to understand the candidate’s experience with complex C# projects and their ability to handle complex programming problems.

In conclusion, these top 10 interview questions are designed to help you understand a candidate’s experience, knowledge, and approach to software development using C# programming. By asking these questions, you can find a senior C# engineer who is capable of designing, developing, and optimizing C# applications effectively.