Where is samples repository for Amplify Gen2 backend?

I apologize, but I don't have specific information about a samples repository for Amplify Gen2 backend that matches your description. The documentation you're referring to with examples of DynamoDB calls via AppSync is not directly mentioned in the sources I have available.

However, I can provide some general guidance based on the available information about AWS Amplify Gen2:

1. AWS Amplify Gen2 uses a TypeScript-based, code-first approach for defining backends. This means that instead of a separate repository of samples, you typically define your data model, business logic, and API calls directly in your project files.

2. For a practical example, there is a recipe generator app that uses Amplify Gen2. While it's not specifically focused on DynamoDB operations, it does demonstrate how to set up a backend with Amplify Gen2. You could fork and clone this repository to explore its structure:

   https://github.com/aws-samples/recipe-ai

3. In a typical Amplify Gen2 project, you would define your data schema in a file like amplify/data/resource.ts. This file would contain the definitions for your data models and the operations you want to perform.

4. To see actual database operations, you would need to deploy your backend to a sandbox environment using the command npx amplify sandbox. This creates a cloud environment where you can test your backend operations.

5. If you're looking to understand how the backend interacts with DynamoDB, you might want to explore the amplify/backend.ts file in your project, which typically contains the configuration for your data sources.

If you're still having trouble finding specific examples or a repository that demonstrates DynamoDB operations via AppSync in Amplify Gen2, I would recommend reaching out to the AWS Amplify team through their official channels or community forums for more targeted assistance.
Sources
Concepts - AWS Amplify Gen 2 Documentation
Use Generative AI and Next.js with AWS Amplify to build a Fullstack Recipe Generator | Front-End Web & Mobile
Quickstart - AWS Amplify Gen 2 Documentation