In a jQuery app, you can store model data using various methods, depending on the complexity of your data and the needs of your application. Here are a few options:

1. JavaScript Objects: You can create JavaScript objects to store your model data. Objects can be nested, allowing you to organize your data in a structured manner. You can use object properties to store data attributes and values, and use methods to manipulate the data. This approach is useful for simple applications with relatively small amounts of data.

2. JSON: JavaScript Object Notation (JSON) is a lightweight data interchange format that is easy to read and write. You can use JSON to store your model data as a string, and then parse it back into a JavaScript object when you need to access or manipulate the data. JSON is commonly used to exchange data between the server and client, but it can also be used to store data in the client-side of a jQuery app.

3. HTML Data Attributes: You can use HTML data attributes to store model data directly in the HTML markup of your application. This approach is useful for small amounts of data that are associated with specific HTML elements, such as form fields or buttons. You can use jQuery methods such as .data() to retrieve and manipulate the data.

4. Local Storage: Local storage is a web storage mechanism that allows you to store key-value pairs in the client’s web browser. You can use local storage to store model data that needs to persist between user sessions or page refreshes. Local storage is limited to a few megabytes per domain, but it is useful for caching data that is expensive to retrieve or compute.

5. AJAX: Asynchronous JavaScript and XML (AJAX) is a technique that allows you to load and update data asynchronously without reloading the entire page. You can use AJAX to retrieve model data from the server in JSON format and then update your jQuery app’s model with the data. AJAX is useful for applications with complex data that requires dynamic updates and synchronization between the client and server.

Overall, the choice of data storage method depends on the requirements and architecture of your jQuery app. You should choose the method that best suits your data model, data access patterns, and performance requirements.