Which tool should be utilized to diagnose problems within the application code without redeploying the application?

To diagnose problems within application code without the need for redeployment, utilizing Stackdriver Debug Logpoints is the most effective option. Logpoints allow developers to insert logging statements into live applications without modifying the code or redeploying the application. This capability is particularly useful for troubleshooting and identifying issues in a production environment where it may not be feasible or safe to alter the code directly.

By setting logpoints, developers can capture data at specific points during execution, thus gaining insights into variable states, application flow, and any anomalies without impacting the application's availability. This tool enables a more agile and responsive debugging process, allowing teams to address problems quickly and efficiently.

In contrast, Stackdriver Trace is used primarily for performance monitoring and latency analysis, providing insight into how requests are processed across different services. Stackdriver Monitoring focuses on tracking the health and performance of applications and infrastructure, rather than diagnosing code-specific issues. Stackdriver Debug Snapshots capture the state of the application at specific moments, but they still require code changes to function effectively, thus necessitating a redeploy in certain scenarios.